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Objectives: While Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA), defined as CC398, is a well-known pathogen among those working with livestock, there are indications that LA-MRSA prevalence among the general population is increasing. However, the clinical impact in urban areas remains unknown. The aim of this study was to assess the genetic epidemiology and clinical characteristics of LA-MRSA in an urban area with a limited livestock population., Methods: In this retrospective study, we evaluated LA-MRSA strains that were collected between 2014 and 2018 from patients who received clinical care in a single urban area in Netherlands. Patient files were assessed for livestock exposure data, clinical findings, and contact tracing information. Next-generation sequencing (NGS) analysis in combination with wgMLST was conducted to assess genetic diversity and relatedness and to detect virulence and resistance genes., Results: LA-MRSA strains were cultured from 81 patients, comprising 12% of all the MRSA strains found in seven study laboratories between 2014 and 2018. No livestock link was found in 76% of patients ( n = 61), and 28% of patients ( n = 23) had an infection, mostly of the skin or soft tissue. Contact tracing had been initiated in 14 cases, leading to the identification of two hospital transmissions: a cluster of 9 cases and one of 2 cases. NGS data were available for 91% ( n = 75) of the patients. wgMLST confirmed the clusters detected via contact tracing ( n = 2) and identified 5 additional clusters without a known epidemiological link. Relevant resistance and virulence findings included the PVL virulence gene (3 isolates) and tetracycline resistance (79 isolates)., Conclusion: LA-MRSA may cause a relevant burden of disease in urban areas. Surprisingly, most infections in the present study occurred in the absence of a livestock link, suggesting inter-human transmission. These findings and the presence of PVL and other immune evasive complex virulence genes warrant future surveillance and preventative measures., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Konstantinovski, Schouls, Witteveen, Claas, Kraakman, Kalpoe, Mattson, Hetem, van Elzakker, Kerremans, Hira, Bosch and Gooskens.)

The introduction of standardized matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) platforms in the medical microbiological practice has revolutionized the way microbial species identification is performed on a daily basis. To a large extent, this is due to the ease of operation. Acquired spectra are compared to profiles obtained from cultured colonies present in a reference spectra database. It is fast and reliable, and costs are low compared to previous diagnostic approaches. However, the low resolution and dynamic range of the MALDI-TOF profiles have shown limited applicability for the discrimination of different bacterial strains, as achieved with typing based on genetic markers. This is pivotal in cases where certain strains are associated with, e.g., virulence or antibiotic resistance. Ultrahigh resolution MALDI-FTICR MS allows the measurement of small proteins at isotopic resolution and can be used to analyze complex mixtures with increased dynamic range and higher precision than MALDI-TOF MS, while still generating results in a similar time frame. Here, we propose to use ultrahigh resolution 15T MALDI-Fourier transform ion cyclotron resonance (FTICR) MS to discriminate clinically relevant bacterial strains after species identification performed by MALDI-TOF MS. We used a collection of well characterized Pseudomonas aeruginosa strains, featuring distinct antibiotic resistance profiles, and isolates obtained during hospital outbreaks. Following cluster analysis based on amplification fragment length polymorphism (AFLP), these strains were grouped into three different clusters. The same clusters were obtained using protein profiles generated by MALDI-FTICR MS. Subsequent intact protein analysis by electrospray ionization (ESI)-collision-induced dissociation (CID)-FTICR MS was applied to identify protein isoforms that contribute to the separation of the different clusters, illustrating the additional advantage of this analytical platform.

Resistance to ciprofloxacin in Escherichia coli is increasing parallel to increased use of fluoroquinolones both in The Netherlands and in other European countries. The objective was to investigate the contribution of active efflux and expression of outer membrane proteins (OMPs) in a collection of clinical E. coli isolates collected at a clinical microbiology department in a Dutch hospital. Forty-seven E. coli isolates a wide range of ciprofloxacin minimum inhibitory concentrations and known mutations in the quinolone resistance determining region were included. A fluorometric determination of bisbenzimide efflux was used two different efflux pump inhibitors and compared to quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for the expression levels of acrA, acrB, tolC, yhiV, and mdfA efflux pump genes and the OMPs ompF and ompX. Six isolates (12.7%) showed increased efflux. Although in 35 isolates (76%), overexpression of ≥1 efflux pump genes using qRT-PCR was present. Only the combined overexpression of acrAB-TolC and mdfA correlated with the phenotypic efflux assay using glucose/carbonyl cyanide m-chlorophenylhydrazone with glucose. Thus, efflux was involved in ciprofloxacin resistance in a limited number of E. coli isolates collected at a clinical microbiology department in a Dutch hospital complementing other resistance mechanisms.

A prospective cohort study was performed among travelers from the Netherlands to investigate the acquisition of carbapenemase-producing Enterobacteriaceae (CP-E) and extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-E) and associated risk factors. Questionnaires were administered and rectal swab samples were collected and tested before and after traveler return. Of 370 travelers, 32 (8.6%) were colonized with ESBL-E before trave,; 113 (30.5%) acquired an ESBL-E during travel, and 26 were still colonized 6 months after return. No CP-E were found. Independent risk factors for ESBL-E acquisition were travel to South and East Asia. Multilocus sequence typing showed extensive genetic diversity among Escherichia coli. Predominant ESBLs were CTX-M enzymes. The acquisition rate, 30.5%, of ESBL-E in travelers from the Netherlands to all destinations studied was high. Active surveillance for ESBL-E and CP-E and contact isolation precautions may be recommended at admission to medical facilities for patients who traveled to Asia during the previous 6 months.

Objectives: To characterize the mechanisms of fluoroquinolone and cephalosporin resistance in Enterobacteriaceae from a Dutch teaching hospital in 2008., Methods: We sequenced gyrA, gyrB, parC and parE. The presence of plasmid-encoded genes qnrA, qnrB, qnrS, aac(6')-Ib, qepA, bla(TEM), bla(SHV,) bla(OXA), bla(CTX-M) and bla(AmpC) was studied by PCR. Escherichia coli isolates were further characterized by AFLP and multilocus sequence typing (MLST)., Results: In total, 49 E. coli, 16 Klebsiella pneumoniae and 3 Enterobacter cloacae isolates were investigated. Mutations in gyrA were found in all E. coli isolates. Forty-five (92%) E. coli isolates carried at least one point mutation in parC. Most E. coli isolates (59%) also carried mutations in parE, of which I529L was the most prevalent. I529L was unequivocally associated with E. coli sequence type (ST) 131. This single-nucleotide polymorphism (SNP) was later also found in eight out of nine ST131 strains from another collection. Twenty-nine E. coli isolates carried extended-spectrum β-lactamase (ESBL) genes, predominantly bla(CTX-M-15). In E. coli, aac(6')-Ib-cr was the predominant plasmid-mediated resistance mechanism, whereas in K. pneumoniae qnr genes were found mostly. In K. pneumoniae isolates, qnr and aac(6')-Ib-cr co-occurred with ESBL genes (n = 13; bla(CTX-M) and bla(SHV)) and/or bla(AmpC) (n = 3; bla(DHA-1))., Conclusions: E. coli ST131 was the predominant clone, which accumulated a high number of chromosomal mutations. The I529L SNP in parE was a signature of most, but not all, ST131 strains. In contrast to E. coli, fluoroquinolone resistance mechanisms were predominantly plasmid-encoded in K. pneumoniae.

Over a two-week period in November 2006, vancomycin-resistant Bacillus cereus was isolated from respiratory samples from six ventilated paediatric intensive care unit (PICU) patients. To investigate the possibility of a common source and extent of the dissemination, all procedures related to mechanical ventilation were monitored and surveillance cultures performed. B. cereus was isolated from reusable air-flow sensors, before and after on-site disinfection with 70% alcohol. The organism was also isolated from respiratory samples from three other ventilated patients and from two ventilation grids in the ceiling of PICU, as well as from the alcohol solution itself. Using amplified fragment length polymorphism (AFLP) typing, B. cereus strains from the six PICU patients together with isolates recovered from the air-flow sensors and the alcohol solution were shown to be closely related. Isolates from the ventilation grids demonstrated different AFLP patterns to the outbreak strain. Intervening measures, including disinfection by autoclaving all reusable air-flow-guiding parts and the use of disposable non-autoclavable parts, resulted in rapid termination of the outbreak. B. cereus infections can cause significant morbidity, particularly in intensive care patients. Disinfection of all air-flow-guiding reusable parts for mechanical ventilation should be addressed with great care and should include effective autoclaving in order to eradicate spores.

X-linked agammaglobulinaemia (XLA) is an immunodeficiency caused by mutations in Bruton's tyrosine kinase (Btk) and is characterized by an almost complete arrest of B cell development. We analysed expression of Btk in B lymphoblastoid cell lines (BLCL) derived from four unrelated XLA patients. In one patient, with a 3 x 5 kb genomic deletion encompassing the first (untranslated) exon, mRNA levels and in vitro kinase activities were very low. The patient manifested a mild phenotype with a delayed onset of the disease. Another mutation, in which the intron 3 donor splice site is lost, was also associated with very low mRNA levels and an absence of detectable Btk protein. Patients with this mutation showed extensive heterogeneity of the immunological phenotype. In the BLCL of a third patient, with an Arg288 substitution in the SH2 domain, the mutation did not appear to affect the expression level, nor to abrogate in vitro phosphorylation activity. In the BLCL of the fourth patient, with an Arg28 mutation in the PH domain, tyrosine kinase activity in BTK precipitates appeared to be decreased compared with control BLCL.

A 13-year-old boy with immunodeficiency with hyper-IgM was analyzed for mutations in the CD40L gene. An insertional mutation of an extra T in a run of four T's was found in the second exon of the gene, leading to a premature translation stop. Genetic counselling of the family was performed, based on mutation detection by PCR/oligohybridization.

X-linked agammaglobulinemia (XLA) is an inherited immunodeficiency disease in man, reflecting an arrest in differentiation of pre-B cells to mature B cell stages. The gene defective in XLA has been identified as a cytoplasmic protein tyrosine kinase, named btk (Bruton's tyrosine kinase). Here we report the characterization of mutations in the btk gene of five unrelated XLA families. Amplified products were generated from cDNA, cloned and sequenced. Three single point mutations and two small insertions were identified. One of the point mutations and the two insertions created stop codons that would lead to truncated btk proteins. In one XLA patient we found a single basepair substitution that altered the highly conserved Arg288 within the SH2 domain and would therefore abrogate interactions with substrate phosphotyrosines. In another XLA patient a single basepair substitution was observed that altered the conserved Arg28 residue in the N-terminal unique region of unknown function. This residue is also mutated in the xid mouse, which has a different, less severe, B cell deficiency. We conclude that a similar mutation in the btk gene leads in man to an almost complete arrest at an early stage of B cell differentiation, but in the mouse to only limited B cell abnormalities.

X-linked agammaglobulinemia (XLA) is an immunodeficiency disease in man, resulting from an arrest in early B cell differentiation. The gene defective in XLA has recently been identified and encodes a cytoplasmic protein tyrosine kinase, named Bruton's tyrosine kinase (btk), essential for cell differentiation and proliferation at the transition from pre-B to later B cell stages. In this study we investigated btk expression by Northern blotting experiments in a series of human (precursor-) B cell lines, acute lymphoblastic leukemias and plasmacytomas. btk was found to be already expressed in very early stages of B cell differentiation, even prior to immunoglobulin (Ig) heavy (H) or light (L) chain gene rearrangements. Transcripts were also detected at the pre-B cell stage and in mature B cells, irrespective of the Ig H chain class expressed. Approximately at the transition from mature B cells to plasma cells, expression of the btk gene is down-regulated. In addition, the btk gene was found to be expressed in myeloid cell lines and acute myeloid leukemias. btk expression in myeloid cells is probably not a prerequisite for myeloid differentiation, since myeloid cells in XLA patients seem not to be affected. No btk expression was found in T-lineage cells. The btk expression profile, i.e. from early precursor-B cell stages preceding Ig rearrangement up to mature B cells, supports the hypothesis that the XLA defect resides in a critical step of B cell development which is independent of the Ig gene recombination machinery.

X-linked agammaglobulinemia (XLA) is a humoral immunodeficiency disease in man, characterized by an arrest in B lymphocyte differentiation at the precursor B cell stage. The structure of expressed immunoglobulin (Ig) kappa light (L) chain rearrangements of nine B lymphoblastoid cell lines from one XLA patient was investigated by amplification of cDNA by the polymerase chain reaction using 5' V kappa family-specific primers and a 3' kappa constant region primer. Members of all four V kappa gene families were found to be utilized in Ig kappa L chain rearrangements at frequencies that were consistent with random V kappa family usage. There was no preference for usage of any particular kappa joining segment. Additional diversity was generated by deletions and random nucleotide insertions at the site of juxtaposition. Particular V kappa members seemed to be overrepresented in the sample. The observed homology of the V kappa I, V kappa II and V kappa III region sequences, both to each other and to known germ-line V kappa sequence indicated the absence of somatic mutations in the majority of these expressed Ig genes. In contrast of the single-member V kappa IV family four different sequences were found to be expressed. That these sequences were mutated derivatives of a germ-line V kappa IV element was substantiated both by sequence analysis and oligonucleotide hybridization. This finding shows that the mutation process can occur in early stages of B cell development i.e. before H chain class switch has occurred. The presence of these mutations is probably independent of clonal expansion since XLA patients are unable to respond to antigen. We conclude that the differentiation arrest in XLA does not preclude early onset of somatic mutation events in V kappa gene segments.

The differential methylation of a CpG island 2.5 kb distant from a hypervariable region at the DXS255 locus provides the basis for a Southern blotting X chromosome inactivation analysis system. The technique enables carrier detection in about 90% of females at risk from pedigrees with Wiskott-Aldrich syndrome, X-linked severe combined immunodeficiency or X-linked agammaglobulinemia.

We evaluated the use of methylation analysis at the DXS255 locus as a method for carrier detection in X-linked severe combined immunodeficiency (XSCID). We also investigated the variations of X inactivation patterns in several haematopoietic cell lineages of XSCID carriers, both within and between XSCID pedigrees.

B lymphoblastoid cell lines (BLCL), established from bone marrow and peripheral blood mononuclear cells from two severe combined immunodeficiency (SCID) patients, manifested a complete absence of genomic rearrangements of the immunoglobulin (Ig) heavy (H) and light (L) chain loci. The BLCL contained germ-line transcripts of the Ig kappa region locus of approximately 1.2 kilobase (kb). By cDNA cloning and sequence analysis the transcripts were shown to consist of a C kappa segment, a J kappa 1 gene segment, 160 base pairs (bp) of J kappa 1 5' intervening sequence, containing the heptamer/nonamer recombination recognition sequences and at the 5' end a 523-bp segment designated human kappa zero, The first 206 bp of this 5' segment were homologous to the reported murine kappa zero region. Genomic restriction mapping and DNA sequence analysis demonstrated that the human kappa zero segment is located approximately 4 kb upstream of J kappa 1. The kappa zero segment contains a putative promoter region with an OCT2 binding site, and has a splice donor site to accomplish splicing to an acceptor site 160 bp upstream of J kappa 1. Expression of the kappa zero gene segment was found in BLCL derived from normal fetal bone marrow, in which both Ig kappa loci were in the germ-line configuration. These findings indicate that the described transcripts are not only present in SCID, but also in normal developing pre-B lymphocytes. The expression of germ-line Ig kappa L chain transcripts may be associated with the locus becoming accessible to gene rearrangement.

The patterns of X chromosome inactivation were determined in 14 females from three unrelated X-linked severe combined immunodeficiency (XSCID) pedigrees. All the females were found to be heterozygous for the hypervariable DXS255 locus, enabling analysis of differential methylation of this locus in peripheral blood haematopoietic cells. All six obligate carriers manifested a unilateral X chromosome inactivation in the T lymphocyte population. Differential methylation analysis of T lymphocytes was subsequently applied to establish the carrier status of females at risk in the XSCID pedigrees. In the B lymphocyte population of four XSCID carriers a unilateral X chromosome inactivation was observed. Four other carriers had minor fractions and one carrier had a substantial fraction of B lymphocytes with the XSCID gene defect on the active X chromosome. Within single XSCID pedigrees the carriers manifested different patterns. In two pedigrees the granulocyte populations of all carriers showed a random distribution of X chromosome inactivation. In the third pedigree the granulocytes of the three carriers analyzed manifested complete inactivation of the X chromosome that carried the XSCID mutation, exposing a selective disadvantage of granulocytes that express the XSCID defect. The pedigree-dependent differences in the involvement of the granulocyte population suggest the existence of two distinct XSCID defects.

The degree of methylation at the 5' and 3' CCGG sequences flanking the variable number of tandem repeat (VNTR) region of the DXS255 locus at Xp11.22 was analysed separately in several haematopoietic cell lineages. The 5' CCGG site on active chromosomes was found to be completely methylated in B and T lymphocytes and granulocytes. Methylation of the 5' site on inactive X chromosomes differed between females (0%-60%), but was consistent in different cell lineages obtained from individual females. In contrast, methylation at the 3' CCGG site on active chromosomes was found to vary in B lymphocytes (40%-100%), whereas complete methylation was found in T lymphocytes and granulocytes. The extent of methylation on inactive X chromosomes was found to differ significantly between B lymphocytes (17%), T lymphocytes (54%) and granulocytes (82%). Thus, methylation at the 5' CCGG site seems to be primarily related to the status of X chromosome inactivation, whereas methylation at the 3' CCGG site is mainly subject to cell-lineage-specific influences.

X-linked agammaglobulinemia (XLA) is characterized by an arrest in early B lymphocyte differentiation. Precursor B cells are present in the bone marrow (BM), whereas peripheral blood B cell numbers are severely decreased. A series of Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell lines (BLCL) was established from peripheral blood of three XLA patients belonging to one pedigree. These BLCL manifested productive VHDJH rearrangements and a random utilization of the VH families. The CDR3 regions of the rearrangements varied in length from 12 to 47 nucleotides and included N regions in all cases. The results supported the conclusion that the few B lymphocytes in peripheral blood of XLA patients exhibit all mechanisms that generate immunoglobulin (Ig) heavy (H) chain diversity. However, no evidence for somatic mutation was found. Within the VH3 family 50% of the expressed VH gene segments belonged to a single subgroup and within the VH4 family a preferential utilization of one VH4 gene element was observed. The utilization of H chain joining (HH) elements was biased to JH4 and JH6 and a high percentage of the CDR3 regions was found to be generated by unconventional mechanisms, such as multiple D usage and the fusion of D elements to D segments with irregular recombination recognition signals. These unique features of the recombined and expressed VHDJH regions in XLA may explain the inability of XLA patients to respond to a variety of antigens. Alternatively, they could be secondary to a B lymphocyte maturation defect in XLA.

The Wiskott-Aldrich syndrome (WAS) is characterized by severe recurrent infections, petachiae and chronic eczema. The syndrome involves differentiation disorders in several haematopoietic cell lineages usually manifested as T lymphocyte deficiency, dysgammaglobulinaemia and thrombocytopenia. The defect is inherited in an X-linked recessive mode. A 1-year-old boy presented with otitis, upper respiratory infections, eczema, a persistent granulocytopenia and a dysgammaglobulinaemia. In his family five males in two generations had been shown to have WAS, which entailed a significant risk for the patient to have WAS. As the WAS gene or gene product is not delineated, the symptoms of the patient presented a diagnostic dilemma. If the boy had inherited the disease, his mother should be a WAS carrier. Segregation analysis in the family using the closely linked restriction fragment length polymorphisms (RFLP) DXS7, DXS255 and DXS14 did not exclude her carriership, although the probability was low. As a result of the differentiation arrest, obligate female WAS carriers manifest a unilateral X chromosome inactivation pattern in several haematopoietic cell lineages. Methylation analysis of the X chromosomal DXS255 loci exposed random X chromosome inactivation patterns in the peripheral blood granulocytes, T lymphocytes and B lymphocytes of the patient's mother. These findings excluded her WAS carriership and therefore excluded the diagnosis of WAS in the patient. This was further substantiated in a 1-year follow up with recovery from the haematological and immunological symptoms. These results demonstrated that X inactivation analysis in maternal leucocytes is decisive in the exclusion of the diagnosis of WAS.

X-linked immunodeficiency with hyperimmunoglobulinemia M (XHM) reflects an impairment of the immunoglobulin (Ig) heavy (H) chain class switch of B lymphocytes from IgM to IgG and IgA. XHM is recessive; female carriers manifest normal IgG and IgA production. Due to random X chromosome inactivation in all somatic cells of females, about half of the lymphocytes of XHM carriers are not able to express an intact XHM gene. An intrinsic defect of the Ig H chain class switch mechanism in XHM B lymphocytes would thus lead to a skewed X chromosome inactivation pattern in the IgG- and IgA-expressing B lymphocytes of female carriers. IgM-, IgG- and IgA-expressing B lymphoblastoid cells (BLC) were established by Epstein-Barr virus transformation of peripheral blood mononuclear cells of two female XHM carriers. In an analysis of differential methylation of the polymorphic DXS255 loci, random X chromosome inactivation patterns were found in populations of T lymphocytes, in IgM-expressing B lymphocytes and in IgG- or IgA-expressing B lymphocytes. The heterogeneity of Ig H chain rearrangements and the Ig light chain usage in the IgA- or IgG-expressing BLC clones that had inactivated the X chromosome which carries the intact XHM gene and in BLC clones with the homologous X chromosome inactivated were similar. The results indicated that the intrinsic Ig H chain class switch mechanism in XHM B lymphocytes is fully intact. We conclude that the XHM gene encodes a class switch inducer that is transferred to B lymphocytes.

An autosomal recessive type of severe combined immunodeficiency disease (SCID) was characterized by an absence of immunoglobulins (Ig) in the serum and of Ig+ lymphocytes in bone barrow (BM) and peripheral blood. In the BM CD10+/terminal deoxynucleotidyl transferase-positive lymphocytes were identified. Epstein-Barr virus-transformed B lymphoblastoid cell lines (BLCL) obtained from BM and peripheral blood did not synthesize Ig. The Ig heavy and light chain gene complexes in the BLCL had retained the germ-line configuration. Mature T cells were present but their numbers in peripheral blood were decreased. T lymphoblastoid cells derived from peripheral blood expressed normal T cell receptor (TcR) CD3 complexes and manifested various genomic TcR rearrangements. It was concluded that this type of SCID entailed a complete arrest of B lymphocyte differentiation in an early stage prior to Ig rearrangements and a quantitative defect of T lymphocytes which nevertheless allowed development of mature T cells. Repeated failures of BM transplantation and the striking absence of Ig assembly suggested that this SCID defect resides in the BM microenvironment.

The involvement of DNA methylation in aberrant MHC class II gene expression in EBV-transformed B-cell lines from 2 patients (THF and DGN) with the MHC class II deficiency syndrome (bare lymphocyte syndrome) was investigated. Incubation of the cells in the presence of various concentrations of 5-azadeoxycytidine resulted in the induction of expression of HLA DR genes in the DGN cell line, whereas, in the THF cell line, no effect of 5-azadeoxycytidine treatment on the expression of the HLA DR genes could be detected. Subsequent Southern blot analysis using methylation-sensitive restriction enzymes (ApyI, EcoRII and HhaI) and 5-azadeoxcycytidine-treated and untreated genomic DNA, indicated that the lack of HLA DR-A expression in the DGN cell line is not caused by hypermethylation of the 5' region of the HLA DR-A gene. These results indicate that 5-azadeoxycytidine treatment of the DGN cell line leads to activation of a methylation-sensitive factor that is involved in the regulation of transcription of the DR-A gene. In cell line THF, however, demethylation does not restore the activity of this factor. The lack of MHC class II expression in this cell line is caused by some other defect. The results of our analysis indicate that at least two different factors are involved in regulation of MHC class II gene expression.

X-Linked agammaglobulinemia (XLA) is a severe antibody deficiency disease in man, resulting from an arrest in differentiation of pre-B cells. XLA is recessive: female carriers do not exhibit antibody deficiency, but manifest an exclusive inactivation of the XLA-carrying X chromosome in all peripheral blood B lymphocytes. An exclusive inactivation of the paternal X chromosome in the B lymphocytes of all daughters of a male who had no agammaglobulinemia demonstrated that the XLA defect can originate from healthy males. These males are X chromosomal mosaics. X-Chromosomal RFLP segregation analyses in other XLA pedigrees suggest a frequent introduction of XLA by healthy males. This implies that XLA often originates from mitotic errors, either at postmeiotic or early postzygotic stages.

X-linked agammaglobulinemia (XLA) is a severe antibody deficiency disease reflecting an arrest of B lymphocyte differentiation at the level of precursor B cells. The disease is inherited in an X-linked recessive mode. In a single eight-generation pedigree the XLA gene was mapped to the Xq21.3-Xq22 area of the X chromosome. The data establish close linkage of the XLA locus to the DXS17 restriction fragment length polymorphic (RFLP) marker locus (the lod score exceeding 6 at phi = 0). A series of RFLP markers around the DXS17 locus provided an RFLP haplotype of use in genetic counselling within this pedigree. In one other pedigree a phenotypically identical disease was inherited but was accompanied by a high frequency of recombination with the DXS17 locus, which made localisation of the gene at the DXS17 locus highly unlikely (lod score less than -3). This genetic heterogeneity complicates genetic counselling within particular pedigrees, especially when the localization of the XLA gene involved in those pedigrees has not been established.

A series of polyclonal and monoclonal anti-human IgE sera reacted with a panel of 11 selected IgA and IgM producing B lymphoblastoid cell lines (BLCLs) in cytoplasmic fluorescence, ELISA and immunoprecipitation assays. The reactions were discordant between the BLCLs and the individual antisera. The panel of 11 BLCLs was selected from over 500 BLCLs by an ELISA spot assay using a polyclonal anti-human IgE serum. The BLCLs produced exclusively IgM or IgA, both with either kappa or lambda light chains as shown by immunoprecipitation/PAGE and mRNA analyses. The data indicate that IgE antisera may recognize IgE-like epitopes on the variable parts of some IgM or IgA molecules. These reactivities of IgE antisera may lead to false positive results of serum IgE determinations. Selected BLCLs are useful targets for exposing such reactivities in IgE antisera.

The gene involved in X-linked immunodeficiency with hyperimmunoglobulinemia M (XHM) was localized by the use of nine restriction fragment length polymorphic (RFLP) markers covering the entire X chromosome. Multipoint linkage analysis of RFLP data obtained in a three generation XHM pedigree indicates the Xq24-q27 area around the DXS42 RFLP locus as the most likely localization of the XHM locus.

The hyper-IgG1(A1) syndrome entails a polyclonal selective increase of the serum levels of immunoglobulin (Ig) G1 and to a lesser extent of IgA1; this is not mediated by malignancy, infectious or autoimmune diseases or environmental agents. In three generations of a family, all the affected individuals carried an immunoglobulin heavy chain (IgH) allele distinguished by restriction fragment length polymorphism analysis; the IgH allele was not present in non-affected family members. A 32:1 chance for the linkage of this rare IgH haplotype with the hyper-IgG1(A1) syndrome in the family argues for a dominant regulator located at the human IgH locus having a selective influence on the production of IgG1 and IgA1.