Search

Purpose: This study sought to investigate how frequently applicants to internal medicine (IM) and pediatrics fellowships are subjected to prohibited questions, how correlates of these interview questions compare between IM and pediatrics fellowship applicants, and which applicant subgroups are most affected., Method: The National Resident Matching Program (NRMP) emailed an anonymous survey to all applicants for the 2021 appointment year to the Medical Specialties Matching Program (i.e., IM fellowship Matches) and Pediatric Specialties Fellowship Match who certified rank order lists (ROLs). The survey addressed specific questions regarding the use of legally prohibited questions and questions that violate the NRMP's Match Participation Agreement during interview-related activities. Experiences of respondents were compared by preferred subspecialty and respondent demographics within IM and pediatrics., Results: The final response rates of IM and pediatrics fellowship applicants who certified ROLs, including complete and partial surveys, were 21.7% (1,483/6,847) and 23.4% (385/1,648), respectively. Of the IM and pediatrics respondents, 432/1,296 (33.3%) and 97/366 (26.5%), respectively, reported being asked at least one prohibited demographic question. The most commonly asked prohibited questions pertained to relationship or marital status (IM: 312/1,296, 24.1%; pediatrics: 69/367, 18.8%), national origin (IM: 200/1,296, 15.4%; pediatrics: 30/365, 8.2%), and family planning (IM: 104/1,288, 8.1%; pediatrics: 14/366, 3.8%). Nearly 25% of IM and pediatrics respondents reported being asked to identify other programs they applied to or interviewed with. Most often, these questions came from program faculty (IM: 238/303, 78.5%; pediatrics: 69/88, 78.4%) or program directors (IM: 84/303, 27.7%; pediatrics: 18/88, 20.5%)., Conclusions: Substantial proportions of IM and pediatrics fellowship applicants reported being asked prohibited questions during fellowship interview-related activities. Additional educational efforts are needed to eradicate such questions from the interview process., (Copyright © 2024 the Association of American Medical Colleges.)

Background Standardized letters of recommendation (SLOR) have become common features of the medical school to residency transition. Research has shown many advantages over the narrative letter of recommendation including improved letter-writing efficiency, ease of interpretation, and improved reliability as performance predictors. Currently, at least four specialties require fellowship SLORs. Internal medicine adopted its SLOR in 2017. Previous research showed fellowship program directors' satisfaction with the 2017 guidelines. Little is known about residency program directors' acceptance and adherence to the guidelines. Objectives The study sought to assess the adoption rate of each component, barriers to adoption, time commitment, and alignment with intended goals of the guidelines. Methods Anonymous survey links were posted to an internal medicine discussion forum prior to the guidelines in spring 2017 and twice following the guidelines in fall 2018 and winter 2019. Two-sample tests of proportions were used to compare respondent characteristics with known survey population data. Pre- and post-survey comparisons were assessed for statistical significance with Pearson chi-squared statistic. Results The response rate varied from 30% to 35% for each survey period. Medical knowledge, patient care, interpersonal and communication skills, professionalism, and scholarly activity were reported frequently (>96%) at baseline. Inclusion of residency program characteristics, systems-based practice, practice-based learning and improvement, and skills sought to master increased over the study period. Conclusions The new guidelines improved uniform reporting of all core competency data. Overall, the gains were modest, as many pre-survey respondents reported high rates of including components within the guidelines., Competing Interests: No potential conflict of interest was reported by the authors., (© 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Greater Baltimore Medical Center.)

Competing Interests: POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.

Background : In May 2017, the Alliance for Academic Internal Medicine (AAIM) published guidelines intending to standardize and improve internal medicine residency program director (PD) letters of recommendation (LORs) for fellowship applicants. Objectives : This study aimed to examine fellowship PDs impressions of the new guidelines, letter writers' adherence to the guidelines, and the impact of LORs that conformed to guidelines compared to non-standardized letters. Methods : The authors anonymously surveyed fellowship PDs from January to March 2018 to gather input about LORs submitted to their programs during the 2017 fellowship application cycle. Results : A total of 78% of survey respondents were satisfied with letters that followed the AAIM guidelines, whereas 48% of respondents were satisfied with letters that did not. Fellowship PDs felt that letters that followed the AAIM guidelines were more helpful than letters that did not, especially for differentiating between applicants from the same institution and for understanding residents' performance across the six core competency domains. Fellowship PDs provided several suggestions for residency PDs to make the LORs even more helpful. Conclusion : Fellowship PD respondents indicated that LORs that followed the new AAIM guidelines were more helpful than letters that did not.

The American Society of Hematology (ASH)/ASCO Curricular Milestones is a tool for assessment and teaching for fellows in hematology/oncology. The expectations of the Next Accreditation System of the Accreditation Council of Graduate Medical Education (ACGME) was developed over years from the creation of the six core competencies in 1999 to the current data-driven outcomes-based system. The current internal medicine subspecialty milestones (ACGME reporting milestones) follow the general rubric of the general internal medicine milestones. The ASH/ASCO curricular milestones were developed from the foundational elements of the specialty, and they are interwoven with the ACGME reporting milestones. The 2017 ACGME Milestones Report shows that the milestones display progression in performance through clear anchors. Educational outcomes are available in many specialties. The internal medicine subspecialties have been given the opportunity to update the ACGME reporting milestones. The ACGME has acknowledged that these milestones may be different for each of the specialties. The program committees of ASH and ASCO agree that revision of the ACGME reporting milestones would decrease the overlap of domains, lack of clarity, and negative language that is present in version 1.0. ASH and ASCO are working with the ACGME and American Board of Internal Medicine (ABIM) to develop Curricular Milestones, version 2.0.

Some internal medicine residency program directors have expressed concerns that their third-year residents may have been subjected to inappropriate communication during the 2016 fellowship recruitment season. The authors sought to study applicants' interpersonal communication experiences with fellowship programs. Many respondents indicated that they had been asked questions that would constitute violations of the National Residency Matching Program (NRMP) Communications Code of Conduct agreement, including how they plan to rank specific programs. Moreover, female respondents were more likely to have been asked questions during interview experiences about other programs to which they applied, and about their family plans. Post-interview communication policies were not made clear to most applicants. These results suggest ongoing challenges for the internal medicine community to improve communication with applicants and uniform compliance with the NRMP communications code of conduct during the fellowship recruitment process., Competing Interests: No potential conflict of interest was reported by the authors.​

The Accreditation Council for Graduate Medical Education's Next Accreditation System requires training programs to demonstrate that fellows are achieving competence in medical knowledge (MK), as part of a global assessment of clinical competency. Passing American Board of Internal Medicine (ABIM) certification examinations is recognized as a metric of MK competency. This study examines several in-training MK assessment approaches and their ability to predict performance on the ABIM Hematology or Medical Oncology Certification Examinations. Results of a Hematology In-Service Examination (ISE) and an Oncology In-Training Examination (ITE), program director (PD) ratings, demographic variables, United States Medical Licensing Examination (USMLE), and ABIM Internal Medicine (IM) Certification Examination were compared. Stepwise multiple regression and logistic regression analyses evaluated these assessment approaches as predictors of performance on the Hematology or Medical Oncology Certification Examinations. Hematology ISE scores were the strongest predictor of Hematology Certification Examination scores (β = 0.41) (passing odds ratio [OR], 1.012; 95 % confidence interval [CI], 1.008-1.015), and the Oncology ITE scores were the strongest predictor of Medical Oncology Certification Examination scores (β = 0.45) (passing OR, 1.013; 95 % CI, 1.011-1.016). PD rating of MK was the weakest predictor of Medical Oncology Certification Examination scores (β = 0.07) and was not significantly predictive of Hematology Certification Examination scores. Hematology and Oncology ITEs are better predictors of certification examination performance than PD ratings of MK, reinforcing the effectiveness of ITEs for competency-based assessment of MK.

Background: As the Accreditation Council on Graduate Medical Education (ACGME) deliberates over further limiting duty hours of graduate medical education (GME) trainees, few large-scale studies have shown residents to be satisfied with the effect the 2003 standards have had on clinical care, education outcomes, or working environments. This study measures the effect of the 2003 duty hours limits on resident-reported satisfaction with GME training during their rotations through the Department of Veterans Affairs (VA) medical centers from 2001 through 2007., Method: Self-reported satisfaction with clinical care and education environments were assessed by comparing responses to VA's annual Learners' Perceptions Survey administered before 2003 with responses administered after 2003. To measure duty hours effects on satisfaction, before-after differences were adjusted for covariate biases modeled after an exhaustive covariate search with 10-fold cross-validation. Because nonteaching controls are not available in satisfaction studies, we used a robust differencing variable technique to control before-after differences for trend biases in the simultaneous presence of missing data and possible model misspecification., Results: There were 19,605 responders. Adjusting for covariate and trend biases, after the 2003 ACGME standards, 25% more residents in medicine specialties reported satisfaction with VA clinical environment and 11% more with VA preceptors and faculty. For surgery, 33% more residents reported satisfaction with VA clinical environment and 12% more with VA preceptors and faculty. Satisfaction with working environment was mixed., Conclusions: The 2003 ACGME duty hours standards were associated with improved satisfaction for resident clinical training and learning environments.

Purpose: To develop a survey instrument designed to quantify supervision by attending physicians in nonprocedural care and to assess the instrument's feasibility and reliability., Method: In 2008, the Department of Veterans Affairs (VA) Office of Academic Affiliations convened an expert panel to adopt a working definition of attending supervision in nonprocedural patient care and to construct a survey to quantify it. Feasibility was field-tested on residents and their supervising attending physicians at primary care internal medicine clinics at the VA Loma Linda Healthcare System in their encounters with randomly selected outpatients diagnosed with either major depressive disorder or diabetes. The authors assessed both interrater concurrent reliability and test-retest reliability., Results: The expert panel adopted the VA's definition of resident supervision and developed the Resident Supervision Index (RSI) to measure supervision in terms of residents' case understanding, attending physicians' contributions to patient care through feedback to the resident, and attending physicians' time (minutes). The RSI was field-tested on 60 residents and 37 attending physicians for 148 supervision episodes from 143 patient encounters. Consent rates were 94% for residents and 97% for attending physicians; test-retest reliability intraclass correlations (ICCs) were 0.93 and 0.88, respectively. Concurrent reliability between residents' and attending physicians' reported time was an ICC of 0.69., Conclusions: The RSI is a feasible and reliable measure of resident supervision that is intended for research studies in graduate medical education focusing on education outcomes, as well as studies assessing quality of care, patient health outcomes, care costs, and clinical workload.

Background: Graduate medical education is based on an on-the-job training model in which residents provide clinical care under supervision. The traditional method is to offer residents graduated levels of responsibility that will prepare them for independent practice. However, if progressive independence from supervision exceeds residents' progressive professional development, patient outcomes may be at risk. Leaders in graduate medical education have called for "optimal" supervision, yet few studies have conceptually defined what optimal supervision means and whether optimal care is theoretically compatible with progressive independence, nor have they developed a test for progressive independence., Objective: This research develops theory and analytic models as part of the Resident Supervision Index to quantify the intensity of supervision., Methods: We introduce an explicit set of assumptions for an ideal patient-centered theory of optimal supervision of resident-provided care. A critical assumption is that informed attending staff will use available resources to optimize patient outcomes first and foremost, with residents gaining clinical competencies by contributing to optimal care. Next, we derive mathematically the consequences of these assumptions as theoretical results., Results: Under optimal supervision, (1) patient outcome is expected to be no worse than if residents were not involved, (2) supervisors will avoid undersupervising residents (when patients are at increased risk for poor outcomes) or oversupervising residents (when residents miss clinical opportunities to practice care), (3) optimal patient outcomes will be compatible with progressive independence, (4) progressive development can be inferred from progressive independence whenever residents contribute to patient care, and (5) analytic models that test for progressive independence will emphasize adjusting the association between length of graduate medical education training and supervision for case complexity and clinic workload, but not patient health outcomes., Conclusion: An explicit theoretical framework is critical to measure scientifically progressive independence from supervision using graduate medical education data.

Background: A Resident Supervision Index (RSI) developed by our research team quantifies the intensity of resident supervision in graduate medical education, with the goal of testing for progressive independence. The 4-part RSI method includes a survey instrument for staff and residents (RSI Inventory), a strategy to score survey responses, a theoretical framework (patient centered optimal supervision), and a statistical model that accounts for the presence or absence of supervision and the intensity of patient care., Methods: The RSI Inventory data came from 140 outpatient encounters involving 57 residents and 37 attending physicians during a 3-month period at a Department of Veterans Affairs outpatient clinic. Responses are scored to quantitatively measure the intensity of resident supervision across 10 levels of patient services (staff is absent, is present, participated, or provided care with or without a resident), case discussion (resident-staff interaction), and oversight (staff reviewed case, reviewed medical chart, consulted with staff, or assessed patient). Scores are analyzed by level and for patient care using a 2-part model (supervision initiated [yes or no] versus intensity once supervision was initiated)., Results: All resident encounters had patient care supervision, resident oversight, or both. Consistent with the progressive independence hypothesis, residents were 1.72 (P  =  .019) times more likely to be fully responsible for patient care with each additional postgraduate year. Decreasing case complexity, increasing clinic workload, and advanced nonmedical degrees among attending staff were negatively associated with supervision intensity, although associations varied by supervision level., Conclusions: These data are consistent with the progressive independence hypothesis in graduate medical education and offer empirical support for the 4-part RSI method to quantify the intensity of resident supervision for research, program evaluation, and resident assessment purposes. Before informing policy, however, more scientific research in actual teaching settings is needed to better understand the relationships among patient outcomes, clinic workload, case complexity, and graduate medical education experience in resident supervision and professional development.

Chronic colonization and infection of the lung with Pseudomonas aeruginosa is a major cause of morbidity and mortality in cystic fibrosis (CF) patients. Imundo, et al. determined that CF cells had a higher concentration of an asialoganglioside (asialo-G(M1)), to which both P. aeruginosa and S. aureus bound preferentially. We sought to determine if the expression of mutant CFTR is associated with altered sialylation. Our study of epithelial cells transfected with normal and mutant DeltaF508 CFTR, the defect in the majority of CF patients in the United States, were analyzed by ELISA and FACS analysis of cell membranes labeled with lectins which bind to Neu5Ac. We determined that DeltaF508 CFTR is associated with decreased membrane sialic acid residues in the alpha2, 3 position and increased concentrations of asialo- G(M1). Quantitation of sialic acids released from the cellular membranes demonstrated that the presence of the DeltaF508 CFTR is associated with markedly decreased membrane sialylation, but similar cytoplasmic sialylation. Thus, DeltaF508 defect is correlated with decreased expression of G(M1) and with decreased sialylation of all cell surface structures, and this change occurs during post-translational modification of glycoproteins and glycolipids. This may be one factor involved in the chronic bacterial colonization seen in these patients.

Chimpanzees have greater than 98% genomic sequence homology with humans but have significantly more favorable responses to human immunodeficiency virus (HIV)-1 and hepatitis B virus (HBV) and an apparently low incidence of epithelial malignancy. Although there are few shared major histocompatibility complex (MHC) alleles between human and chimp, there is considerable overlap in binding repertoires for epitopes of HIV-1 and HBV. This indicates that differences in viral handling may be due to involvement of cells other than T lymphocytes. Similar mechanisms may be involved in host response to dysplastic or malignant cells. In seeking to understand these differences, most attention has been focused on comparing and contrasting well-characterized steps in immune response. As an additional possibility, alterations in cell-cell interactions dependent upon sialic acid binding proteins known to be involved in immune responses should also be considered. The lack of a particular sialic acid structure (N-glycolyl neuraminic acid, or Neu5Gc) in humans, due to a gene mutation in an essential synthetic enzyme, has potentially altered the kinetics of cellular responses dependent upon these lectins. The absence of Neu6Gc represents the only known major biochemical difference between humans and chimpanzees.

The sialic acids are major components of the cell surfaces of animals of the deuterostome lineage. Earlier studies suggested that humans may not express N-glycolyl-neuraminic acid (Neu5Gc), a hydroxylated form of the common sialic acid N-acetyl-neuraminic acid (Neu5Ac). We find that while Neu5Gc is essentially undetectable on human plasma proteins and erythrocytes, it is a major component in all the four extant great apes (chimpanzee, bonobo, gorilla and orangutan) as well as in many other mammals. This marked difference is also seen amongst cultured lymphoblastoid cells from humans and great apes, as well as in a variety of other tissues compared between humans and chimpanzees, including the cerebral cortex and the cerebrospinal fluid. Biosynthetically, Neu5Gc arises from the action of a hydroxylase that converts the nucleotide donor CMP-Neu5Ac to CMP-Neu5Gc. This enzymatic activity is present in chimpanzee cells, but not in human cells. However, traces of Neu5Gc occur in some human tissues, and others have reported expression of Neu5Gc in human cancers and fetal tissues. Thus, the enzymatic capacity to express Neu5Gc appears to have been suppressed sometime after the great ape-hominid divergence. As terminal structures on cell surfaces, sialic acids are involved in intercellular cross-talk involving specific vertebrate lectins, as well as in microbe-host recognition involving a wide variety of pathogens. The level of sialic acid hydroxylation (level of Neu5Ac versus Neu5Gc) is known to positively or negatively affect several of these endogenous and exogenous interactions. Thus, there are potential functional consequences of this widespread structural change in humans affecting the surfaces of cells throughout the body.

Sialic acids are important cell-surface molecules of animals in the deuterostome lineage. Although humans do not express easily detectable amounts of N-glycolylneuraminic acid (Neu5Gc, a hydroxylated form of the common sialic acid N-acetylneuraminic acid, Neu5Ac), it is a major component in great ape tissues, except in the brain. This difference correlates with lack of the hydroxylase activity that converts CMP-Neu5Ac to CMP-Neu5Gc. Here we report cloning of human and chimpanzee hydroxylase cDNAs. Although this chimpanzee cDNA is similar to the murine homologue, the human cDNA contains a 92-bp deletion resulting in a frameshift mutation. The isolated human gene also shows evidence for this deletion. Genomic PCR analysis indicates that this deletion does not occur in any of the African great apes. The gene is localized to 6p22-p23 in both humans and great apes, which does not correspond to known chromosomal rearrangements that occurred during hominoid evolution. Thus, the lineage leading to modern humans suffered a mutation sometime after the common ancestor with the chimpanzee and bonobo, potentially affecting recognition by a variety of endogenous and exogenous sialic acid-binding lectins. Also, the expression of Neu5Gc previously reported in human fetuses and tumors as well as the traces detected in some normal adult humans must be mediated by an alternate pathway.

Retroviral insertional mutagenesis can both generate somatic cell mutants and pinpoint the genomic locus associated with a mutant phenotype. In the present study, this approach was applied to Chinese hamster ovary cells (CHO) made susceptible to Moloney murine leukemia virus (MoMuLV) infection by stable expression of an ecotropic retrovirus receptor. These CHO cells were infected with a replication incompetent MoMuLV construct with a promoterless hygromycin phosphotransferase (hygro) gene inserted into the U3 region of the long terminal repeat and a second selectable marker, neomycin phosphotransferase (neo), expressed from an internal promoter. CHO clones containing integrated proviruses were selected with hygromycin or G418, and the subset of these with reduced cell surface Neu5Ac were then selected with wheat germ agglutinin (WGA). The majority of the resulting clones had a phenotype not previously described for WGA-resistant CHO mutants arising spontaneously or from chemical mutagenesis: Neu5Ac was almost completely replaced by Neu5Gc. We have provisionally termed these clones SAP mutants, for sialic acid phenotype. Southern analysis of HindIII digested DNA from four SAP mutants revealed that the MoMuLV provirus is present in a 10.4-kilobase (kb) fragment. Probing with a flanking CHO sequence resulted in equivalent hybridization to a 4.6-kb fragment and the 10.4-kb provirus-containing fragment in all four cases, while uninfected parental cells and non-SAP glycosylation mutants generated in the same retrovirus insertional mutagenesis experiments yielded only the 4.6-kb fragment. Sequencing of the 3'-flanking DNA revealed that each of the four SAP mutants had a unique provirus integration site falling within a 796 bp region of the CHO genome. The frequency with which SAP mutants arise suggests that this may be a preferred site for retrovirus integration.

The changes in expression of sialic acids in Sprague-Dawley rats in the prenatal and early postnatal time period have been examined in multiple organs, both visceral and non-visceral. In all organs examined, there is a dramatic increase in both N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc) shortly after birth. The bulk of the sialic acid is present in the ganglioside fraction in all tissues examined. As total amounts of sialic acid present in gangliosides decrease, the proportion present in the low molecular weight cytosolic fraction increases. A curious observation is that Neu5Ac hydroxylase activity is present at the time of the increase in sialic acid, but its activity does not correlate with Neu5Gc expression after the early postnatal period. This implies that Neu5Gc expression has another level of regulation besides CMP-Neu5Ac hydroxylase activity.

Using high-pressure liquid chromatography (HPLC) and gas-liquid chromatography/mass spectrometry (GLC/MS), we have confirmed the existence of several sialic acid modifications in the adult rat and human colon. The major O-acetylated sialic acid in both species is 9-O-acetyl-N-acetylneuraminic acid; N-glycolylneuraminic acid is a major component of the adult rat colon. Both of these major modifications were found to be developmentally regulated during the perinatal period in the rat. The N-glycolyl modification is present prenatally and disappears rapidly in the postnatal period. It reappears in the preweanling period, reaching levels at weaning comparable to those found prenatally. In contrast, the 9-O-acetyl modification is very low prenatally, and undergoes a marked increase shortly after birth in both the rat and human colon. The difference in the kinetics of appearance of the two modifications suggests that they are independently regulated. Regulation of these modifications seems to be influenced by exposure to bacterial by-products or environmental stimuli. The N-glycolyl modification in the rat colon reappeared at weaning, a time of major change in enteral colonic substances. Spontaneously aborted human fetuses, including three with intrauterine infection at 27, 33, and 35 wk of gestation, showed adult levels of O-acetylation in colonic tissue. Also, although O-acetylation in freshly isolated colon tumor specimens was only somewhat lower than that in the adult normal colon, all established colon cancer cell lines studied showed minimal O-acetylation.

N-Glycolylneuraminic acid (Neu5Gc) is an oncofetal antigen in humans and is developmentally regulated in rodents. We have explored the biology of N-acetylneuraminic acid hydroxylase, the enzyme responsible for conversion of the parent sialic acid, N-acetylneuraminic acid (Neu5Ac) to Neu5Gc. We show that the major sialic acid in all compartments of murine myeloma cell lines is Neu5Gc. Pulse-chase analysis in these cells with the sialic acid precursor [6-3H]N-acetylmannosamine demonstrates that most of the newly synthesized Neu5Gc appears initially in the cytosolic low-molecular weight pool bound to CMP. The percentage of Neu5Gc on membrane-bound sialic acids closely parallels that in the CMP-bound pool at various times of chase, whereas that in the free sialic acid pool is very low initially, and rises only later during the chase. This implies that conversion from Neu5Ac to Neu5Gc occurs primarily while Neu5Ac is in its sugar nucleotide form. In support of this, the hydroxylase enzyme from a variety of tissues and cells converted CMP-Neu5Ac to CMP-Neu5Gc, but showed no activity towards free or alpha-glycosidically bound Neu5Ac. Furthermore, the majority of the enzyme activity is found in the cytosol. Studies with isolated intact Golgi vesicles indicate that CMP-Neu5Gc can be transported and utilized for transfer of Neu5Gc to glycoconjugates. The general properties of the enzyme have also been investigated. The Km for CMP-Neu5Ac is in the range of 0.6-2.5 microM. No activity can be detected against the beta-methylglycoside of Neu5Ac. On the other hand, inhibition studies suggest that the enzyme recognizes both the 5'-phosphate group and the pyrimidine base of the substrate. Taken together, the data allow us to propose pathways for the biosynthesis and reutilization of Neu5Gc, with initial conversion from Neu5Ac occurring primarily at the level of the sugar nucleotide. Subsequent release and reutilization of Neu5Gc could then account for the higher steady-state level of Neu5Gc found in all of the sialic acid pools of the cell.

The influenza C virus (INF-C) hemagglutinin recognizes 9-O-acetyl-N-acetylneuraminic acid. The same protein contains the receptor-destroying enzyme (RDE), which is a 9-O-acetyl-esterase. The RDE was inactivated by the serine esterase inhibitor di-isopropyl fluorophosphate (DFP). [3H]DFP-labeling localized the active site to the heavy chain of the glycoprotein. DFP did not alter the hemagglutination or fusion properties of the protein, but markedly decreased infectivity of the virus, demonstrating that the RDE is important for primary infection. Finally, DFP-treated INF-C bound specifically and irreversibly to cells expressing 9-O-acetylated sialic acids. This provides a probe for a molecule that was hitherto very difficult to study.

Intact human erythrocytes were cross-linked with glutaraldehyde (GA) or dimethyladipimidate (DMA) and tested for their ability to bind [125I]-IgG anti-Rh0(D) and to undergo antibody-mediated hemagglutination. There was no decrease in antibody binding after treatment with GA concentrations up to 1.25% and DMA concentrations up to 1%. Red cells treated with these concentrations of GA and DMA did not agglutinate. The techniques employed to induce agglutination of the cross-linked red cells involved "incomplete" IgG anti-Rho (D) in albumin, "complete" IgM anti-D Rho (D) in saline, and the antiglobulin (Coombs) reaction. The agglutinability of the chemically modified red cells was inversely correlated with the extent of fixation. The dissociation of antibody binding from agglutinability in cross-linked erythrocytes suggests that Rho (D) antigen mobility is required for red cell agglutination. Antigen mobility was manifested by the transition from a relatively monodisperse distribution pattern of Rho (D) antigen sites to one of large aggregates or clusters when agglutination was induced by IgM anti-Rho (D), IgG anti-Rho (D) agglutination of protease modified red cells, and by anti-IgG agglutination of IgG anti-Rho (D)-coated red cells. Antigen clustering was not as prominent in red cells agglutinated by IgG anti-Rho (D) in the presence of albumin. Even though antigen mobility is a prerequisite for antibody-mediated hemagglutination, clustering does not appear to be an absolute requirement. The degree of antigen clustering differs with varying types of agglutination.