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Background: Esophageal respiratory fistulae are abnormal communications between the esophagus and the respiratory system. They are either congenital or acquired. Most acquired esophageal respiratory fistulae are of the esophageal tracheal and esophageal bronchial type and are caused by infections or malignant neoplasms, whereas esophageal pulmonary fistulae are rare., Case Presentation: We report a case of a 72-year-old Caucasian man with squamous cell carcinoma of the lung presenting with abrupt-onset dyspnea during localized mediastinal radiotherapy. His laboratory test results suggested major respiratory infection. A chest x-ray revealed left apical lung radiopacity along with excavated lesions, consistent with secondary tumor infection. No clinical improvement was observed despite antibiotic treatment. A contrast-enhanced computed tomographic scan of the chest confirmed persistent lung infection with unfavorable progression and air in the mediastinum; the latter suggested a fistula from the upper third of the esophagus to the upper left pulmonary lobe. Videofluoroscopy confirmed the diagnosis of an acquired esophageal pulmonary fistula. The patient underwent endoscopy, and an esophageal self-expandable metallic stent was deployed., Conclusions: Esophageal pulmonary fistulae must be suspected whenever patients undergoing local mediastinal radiotherapy present with acute pulmonary complications, particularly pneumonia resistant to antibiotic treatment. Esophageal pulmonary fistulae are diagnosed by means of radiological imaging. Because esophageal respiratory fistulae are acute life-threatening conditions, prompt treatment with an endoscopically placed covered stent proves vital.

Cytotoxic T-lymphocyte (CTL) epitopes within the HIV genome are subject to negative and positive selective pressures, the balance of which influences CTL escape at a given epitope. We investigated whether viral fitness requirements dictate conservation of the HLA-A2 restricted immunodominant epitope SLYNTVATL (SL9). Viral clones incorporating changes throughout the SL9 epitope region were compared to consensus SL9 virus in terms of replication kinetics and relative viral fitness. Constructs recapitulating in vivo SL9-CTL escape variants showed markedly little effect on replication and fitness, as did non-natural conservative mutations targeting immunologically relevant positions of the epitope. Although certain residues of the epitope were constrained by viral requirements, our research reveals that there are multiple SL9 variants that are well tolerated virologically but fail to arise in vivo. In light of this data, assumptions regarding the balance of immune and viral selective pressures on this immunodominant epitope sequence need to be reassessed.

Recent progress has begun to define the interactions and signaling pathways that are triggered during positive selection. To identify and further examine self-peptides that can mediate positive selection, we searched a protein-database to find peptides that have minimal homology with the viral peptide (p33) that activates a defined P14 transgenic TCR. We identified four peptides that could bind the restriction element H-2D(b) and induce proliferation of P14 transgenic splenocytes at high concentration. Two of the four peptides (DBM and RPP) were able to positively select the virus-specific TCR in fetal thymic organ culture but were unable to induce clonal deletion. Reverse-phase HPLC and mass spectrometry demonstrated that these peptides were presented by H-2D(b) molecules on thymic epithelial cell lines. We also examined whether the selecting ligands altered T cell responsiveness in vitro. DBM-selected T cells lost their ability to respond to the positively selecting ligand DBM, whereas RPP-selected T cells only retained their ability to respond to high concentrations of RPP. These results demonstrate that self-peptides that mediate positive selection can differentially "tune" the activation threshold of T cells and alter the functional repertoire of T cells.

The human immunodeficiency virus type 1 (HIV-1)-specific CD4(+) T cell response was investigated in 33 untreated HIV-1-infected individuals, using highly sensitive ELISPOT assays and intracellular flow cytometry. The median frequencies of interferon (IFN)-gamma-producing HIV-1 gag-specific CD4(+) T cells did not correlate significantly with control of viral replication or progression. HIV-1 gag-specific interleukin (IL)-4-producing cells were rarely detected. Circulating frequencies of CD4(+) T cells constitutively producing IL-10, however, were significantly higher in individuals with progression or active replication. In 17 of 30 HIV-1-infected individuals, gag antigen was observed to induce IL-10 production from CD4(+) T cells. In 2 individuals, early treatment of acute HIV-1 infection "rescued" low to undetectable gag-specific IFN-gamma-producing CD4(+) T cell responses and dramatically down-regulated constitutive IL-10 production from circulating CD4(+) T cells. The detection of HIV-1-specific IL-10-inducing CD4(+) T cells in HIV-1-infected individuals suggests that HIV-1 may directly subvert specific immune responses by IL-10 induction.

A vigorous expansion of antigen-specific CD8(+) T cells lacking apparent effector function was observed in a rhesus macaque acutely infected with the simian immunodeficiency virus (SIV) strain SIVmac239. Antigen-specific CD8(+) T cells were identified using antigenic-peptide class I major histocompatibility complex tetramers. As many as 8.3% of CD8(+) cells recognized the Mamu-A*01-associated SIV epitope Gag(181-189) (CTPYDINQM); however, these cells demonstrated no effector function when presented with peptide-incubated targets, as measured by intracellular cytokine staining for gamma interferon (IFN-gamma), interleukin-2 (IL-2) production, or direct cellular lysis. Similar results were observed with three other SIV peptide antigens. Nonresponsiveness did not correlate with apoptosis of the CD8(+) cells, nor were cells from this macaque impaired in their ability to present peptide antigens. Associated with the nonresponsive state was a lack of IL-2 production and decreased IL-2 receptor expression. Exogenous IL-2 treatment for 1 week in the absence of antigenic stimulation restored antigen-specific responses and the quantitative correlation between tetramer recognition and antigen-responsive IFN-gamma secretion. This case report suggests a regulatory mechanism that may impede the effector function of antigen-specific T cells during acute infection with SIV or human immunodeficiency virus in some cases. This mechanism may participate in the failure of the immune system to limit infection.

As part of the ongoing study of natural HIV-1 resistance in the women of the Nairobi Sex Workers' study, we have examined a resistance-associated HLA class I allele at the molecular level. Typing by polymerase chain reaction using sequence-specific primers determined that this molecule is closely related to HLA-A*0214, one of a family of HLA-A2 supertype alleles which correlate with HIV-1 resistance in this population. Direct nucleotide sequencing shows that this molecule differs from A*0214, having a silent nucleotide substitution. We therefore propose to designate it HLA-A*02142. We have determined the peptide-binding motif of HLA-A*0214/02142 by peptide elution and bulk Edman degradative sequencing. The resulting motif, X-[Q,V]-X-X-X-K-X-X-[V,L], includes lysine as an anchor at position 6. The data complement available information on the peptide-binding characteristics of this molecule, and will be of use in identifying antigenic peptides from HIV-1 and other pathogens.

Correlates of resistance to infection by human immunodeficiency virus type 1 (HIV-1) are important for defining potential therapeutic interventions and for prophylactic vaccination. In this study, 11 couples discordant in their HIV-1 infection status were prospectively evaluated for the presence of protective factors. Behavioral characteristics of all subjects entailed a high risk of transmission. Cytotoxic T lymphocyte (CTL) responses against viruses isolated from the infected partner, and against laboratory virus isolates, were detected in 5 (45%) of 11 HIV-negative partners, including a CCR5Delta32-homozygous and a heterozygous subject. No CTL responses were observed in 6 control unexposed subjects. Marked variation in lymphocyte susceptibility to viral infection was noted. Resistance attributable to major histocompatibility complex discordance or anti-major histocompatibility complex antibodies was not identified. These results suggest that a combination of factors, including cellular immunity, viral characteristics, and coreceptor integrity, may be involved in the persistent nontransmission of HIV.

Certain human leukocyte antigens, by presenting conserved immunogenic epitopes for T cell recognition, may, in part, account for the observed differences in human immunodeficiency virus type 1 (HIV-1) susceptibility. To determine whether HLA polymorphism influences HIV-1 susceptibility, a longitudinal cohort of highly HIV-1-exposed female sex workers based in Nairobi, Kenya, was prospectively analyzed. Decreased HIV-1 infection risk was strongly associated with possession of a cluster of closely related HLA alleles (A2/6802 supertype; incidence rate ratio [IRR], 0.45; 95% confidence interval [CI], 0.27-0.72; P=.0003). The alleles in this supertype are known in some cases to present the same peptide epitopes for T cell recognition. In addition, resistance to HIV-1 infection was independently associated with HLA DRB1*01 (IRR, 0.22; 95% CI, 0.06-0.60; P=.0003), which suggests that anti-HIV-1 class II restricted CD4 effector mechanisms may play an important role in protecting against viral challenge. These data provide further evidence that resistance to HIV-1 infection in this cohort of sex workers is immunologically mediated.

In an effort to identify an immunological basis for natural resistance to HIV-1 infection, we have examined serum antibody responses to HLA class I antigens in female prostitutes of the Nairobi Sex Workers Study. Anti-HLA antibodies are known to block HIV infectivity in vitro and can be protective against SIV challenge in macaques immunized with purified class I HLA. Thus, it was postulated that broadly cross-reactive alloantibodies recognizing common HLA alleles in the client population might contribute to the prevention of heterosexual transmission of HIV. In fact, 12% of the women were found to have serum IgG antibodies against class I alloantigens. However, this alloantibody did not correlate with the HIV status of the women and was found in a similar proportion of HIV-positive and HIV-resistant women. The observed levels of alloantibody did not increase with HIV infection in susceptible individuals, suggesting that potential antigenic mimicry between HIV and host HLA class I antigens does not significantly increase levels of anti-class I antibodies. The lack of correlation between serum anti-allo-class I HLA antibodies and the risk of sexual transmission indicates that this humoral immune response is unlikely to be the natural mechanism behind the HIV-resistance phenotype of persistently HIV-seronegative women. This result, however, does not preclude the further investigation of alloimmunization as an artificial HIV immunization strategy.

Searching for mechanisms of natural resistance to HIV infection with which to guide HIV vaccine design, we have examined antibody responses to HLA class I antigens in children of HIV-1-infected mothers. Anti-HLA antibodies are known to block HIV infectivity in vitro and can be protective against SIV challenge in macaques immunized with purified class I HLA. It was hypothesized that alloantibody to maternal HLA in children might contribute to the prevention of mother-to-child transmission of HIV-1. In fact, a surprisingly high proportion of the children examined, 22%, were found to have antibody against class I alloantigens. This alloantibody, however, did not correlate with the HIV status of the children and was found in a similar proportion of children of HIV-negative mothers. The HLA specificity of the antibody was not correlated with noninherited maternal HLA alleles and occurred with a higher frequency in older children. This result suggests environmental factors, rather than exposure to maternal cells, are involved in the formation of the alloantibody. The finding that anti-allo-class I HLA antibodies are not associated with a decreased risk of mother-to-child transmission indicates that this humoral immune response is unlikely to be the natural mechanism that accounts for the lack of transmission observed in many births. This result, however, does not preclude the further investigation of cellular alloimmune responses, or the use of alloimmunization as an artificial HIV immunization strategy.

Antigenic peptides are presented to CD8+T lymphocytes by class I major histocompatibility complex (MHC) molecules. Peptides specifically bind to purified class I molecules in vitro, and to class I molecules on cells at nonphysiological temperatures. We report here the kinetic and equilibrium parameters for the binding of radiolabelled influenza nucleoprotein peptides (NP-Y365-380 and shorter homologues) to the murine H-2Db molecule on intact, viable cells at 37 degrees C. In contrast to earlier reports, we show that peptide binding is rapid and reversible, with dissociation constants ranging from nanomolar to micromolar, suggestive of typical ligand-receptor interactions. Only 10% of cell-surface Db molecules can bind these peptides. To address the relationship between peptide binding and T-cell recognition of the antigen-MHC complex, we determined the minimum number of complexes required to sensitize a target cell for lysis by class I-restricted cytotoxic T-lymphocytes. Our data indicate that EL4 thymoma cells (H-2b) can be sensitized for lysis by cytotoxic T-lymphocytes when as few as 200 class I-peptide complexes (less than 0.08% of surface Db molecules) are present per cell.

Using avidin as a model protein antigen, and biotinylated monoclonal antibodies as a convenient means of forming stable complexes with avidin, we have investigated the adjuvant-independent immunization of three mouse strains, C57BL/6, C3H and (C57BL/6 x C3H)F1, with immunoconjugates targeted to different class II MHC and non-MHC sites. The results confirm the effectiveness of anti-I-Ak and anti-I-Ab immunoconjugates with respect to priming for secondary IgG responses in (H-2b x H-2k)F1 mice, while indicating a lack of response in strains which are homozygous for the targeted allele. In terms of non-MHC targets in the monocyte-macrophage lineage, neither anti-MAC-1 nor anti-MAC-2 immunoconjugates were effective in any of the three strains. However, the 33D1 anti-dendritic cell antibody gave significant responses in all three strains, with the F1 response being more than 10-fold greater than the anti-class II immunoconjugates in either strain. These findings indicate that immunotargeting a protein antigen to a non-MHC determinant on dendritic cells in vivo can be an effective means of inducing an adjuvant-independent serological response, and that this approach can have significant advantages over anti-class II MHC immunotargeting.