Immunoglobulin genes, HLA-B8/DR3, and immune responsiveness to primary immunogen and mitogens in normal subjects

Defective expression of CD95 (FAS/APO-1) molecule suggests apoptosis impairment of T and B cells in HLA-B8, DR3-positive individuals

Activation-induced apoptosis is one of the primary control mechanisms for the negative selection of an immune response, leading to maintenance of immune homeostasis and selective T cell deletion. The interaction between the surface molecule Fas and its ligand (FasL) has been proposed as a primary mechanism initiating T cell apoptosis. The T cell receptor modulates the expression and function of these molecules. Defects in the Fas/FasL apoptosis pathway have been shown to result in autoimmune disease in humans and in murine models. Because subjects carrying the HLA-B8, DR3 haplotype show a number of immune dysfunctions, including membrano-proliferative glomerulonephritis, systemic lupus erythematosus, Graves' disease, and others, we investigated Fas expression on T and B cells, and sensitivity to Fas-mediated apoptosis of activated T cells, to determine whether abnormalities of the Fas pathway might be associated with the development of autoimmune diseases in this group of individuals. Our findings show that B cells and resting T cells from HLA-B8+, DR3+ subjects express markedly reduced levels of Fas compared with those isolated from HLA-B8-, DR3+ individuals. Reduced levels of Fas were also evident on the surface of T cells from HLA-B8+, DR3+ subjects activated in vitro by stimulation with OKT3 and phytohemoagglutinin. Cycling T cells from these subjects, evaluated for apoptotic nuclei by flow cytometry after incubation with a cytolytic anti-Fas mAb, showed a significantly lower percentage of Fas-mediated apoptosis than did those from HLA-B8-, DR3- individuals. Normal levels of apoptosis were restored after exposure to a synthetic ceramide analog (C2). Further elucidation of the interaction of these molecules in autoimmune diseases may lead to better understanding of the pathogenesis of these disorders.

Genetic predisposition to HIV-1 infection and acquired immune deficiency virus syndrome: a review of the literature examining associations with HLA [corrected]

Researchers have been studying the relationship between host HLA type and the immune response to HIV-1 since early in the AIDS epidemic. Although the literature is replete with suggestions of an association, the exact locus and nature is unclear. This article reviews the current HLA-HIV/AIDS literature, providing a complete summary of all significant associations reported in journal articles (N = 30) between 1982 and 1993. Consistent associations with alleles comprising the haplotype DQ2-DR3-B8-Cw7-A1 and AIDS progression support a genetic component in AIDS progression. DQ1-DR1-B35-Cw4-A11 and DR5 also show consistent associations with HIV/AIDS outcomes, although it is unclear whether they are measuring susceptibility to HIV-1 infection, AIDS progression, or both. The question of whether HLA influences susceptibility to HIV-1 infection remains unanswered, as well-designed studies addressing this topic are lacking. Similarly, further studies are needed to clarify if HLA type is associated with KS. Several issues that complicate across-study comparisons are discussed including heterogeneity of both HLA and AIDS, potential confounding by race or risk group, and other biases which may influence results. In addition, several proposed biologic mechanisms are explored.

In vitro cytokine production by HLA-B8,DR3 positive subjects

It is well known that healthy subjects carrying the HLA-B8,DR3 haplotype may show an impairment of immune system, the T cells being the most affected. To gain insight into the mechanism(s) of the impairment displayed by these subjects, efforts have been centered on the study of in vitro cytokine production because of the pivotal role played by these mediators in the activation and control of several immune functions. The available results indicate that the ability to several immune functions. The available results indicate that the ability to produce interleukin-1 (IL-1), IL-2 and the soluble form of its receptor (sIL-2R) is impaired in HLA-B8,DR3 positive healthy subjects. To better characterize the cytokine production capacity of HLA-B8,DR3 positive subjects, we have investigated the pattern of in vitro production of IL-2, sIL-2R, IL-4. IL-6 and gamma-interferon (gamma-IFN) by mononuclear cells from HLA-B8, DR3 positive subjects after phytohaemoagglutinin stimulation. A significant decrease of IL-2, sIL-2R and gamma-IFN production by HLA-B8,DR3 positive subjects was observed. No significant difference was instead found between the HLA-B8,DR3 positive subjects and the negative ones as regards IL-4 and IL-6 production. We suggest that this imbalanced cytokine production may well account for the pattern of immune response that may observed in HLA-B8,DR3 positive subjects, i.e. a normal or increased humoral response in face of a low T cell immune responsiveness.

Defective inducer T-cell function before the onset of insulin-dependent diabetes mellitus

To investigate the possible role of CD4+ T lymphocyte immunoregulatory abnormalities in the pathogenesis of human insulin-dependent diabetes mellitus (IDD), we studied the in vitro function of CD4+ helper/inducer and suppressor/inducer T-cell subpopulations in 25 high risk non-diabetic individuals who tested positive for islet-cell antibodies (ICA). Helper-inducer T-cell function, as measured in the pokeweed mitogen T-B co-culture system, was decreased in the ICA+ subjects in comparison to controls. This abnormality in helper/inducer T-cell function was present for both IgG (P = 0.0001) and IgM (P = 0.004) secretion by B cells. Diminished helper/inducer function correlated with ICA titer (Pearson correlation coefficient -0.44) with subjects having an ICA titer greater than or equal to 40 JDF units demonstrating the most significant disturbances in function (P = 0.01). The helper/inducer T-cell subset percentage was also decreased in ICA+ subjects when compared to matched controls (30 +/- 3% vs 39 +/- 2%; P = 0.02). The abnormality in helper/inducer function was intrinsic to the CD4+ CD45RA+ subset and was not simply due to diminished numbers of helper/inducer T-cells added in the co-culture experiments, since the defect persisted when CD4+ CD45RA+ helper/inducer T-cells were purified and added to B cells as the only source of T-cell help. Our results indicate that ICA+ subjects have functional defects in the helper/inducer subpopulation of CD4+ T-cells. This abnormality may contribute to the pathogenesis of IDD and may provide a novel marker for identifying persons at risk for developing IDD.

Major histocompatibility complex genes influence the outcome of HIV infection. Ancestral haplotypes with C4 null alleles explain diverse HLA associations

Several alleles at multiple HLA loci have been found to be associated with infection with human immunodeficiency virus (HIV): HLA A1; B8, B35; Cw7, Cw4; DR1, DR3 and DQ1, are associated with particular disease manifestations and/or disease progression. Furthermore, in a pilot study we have shown an increase in the frequency of C4 null alleles and suggested that all the reported HLA alleles could reflect association with a limited number of ancestral haplotypes (AHs). On this occasion, we studied 122 Caucasoid patients classified according to Centers for Disease Control (CDC) criteria. The control group consisted of 67 seronegative homosexual or bisexual males at risk of developing HIV infection. C4 null alleles were unequivocally present in 58% of patients in CDC IV compared with 33% of the seronegative subjects (chi 2 = 5.65, p less than 0.05). Furthermore, C4 null alleles could be excluded in only 8% and 16% of CDC III and IV, respectively, but in 30% of the seronegative subjects. An increased frequency of three AHs largely accounted for the increases in C4 null and HLA alleles. To examine the role of specific AHs we undertook a longitudinal analysis of a subgroup of 26 patients who seroconverted under observation. Seventeen of these patients were followed for 32 to 63 months. All seven patients with the 8.1 AH (A1, CW7, B8, BfS, C4AQ0, C4B1, DR3, DQ2) developed low CD4 lymphocyte counts (less than 450 x 10(6)/l) compared with only 2 of 10 patients without this haplotype (p less than 0.002). All three deaths occurred in patients with the 8.1 AH. The acquired immunodeficiency syndrome developed in three further cases with either 8.1- or B35-bearing (35.x) haplotypes. Sequential CD4/8 ratios showed an early and progressive decline in individuals with 8.1 or 35.x. Since the 8.1 and 35.x AHs contain deletions of the central major histocompatibility complex (MHC) genes, we suggest that the genes affecting HIV infection and progression are within the central MHC region.

HLA-B8,DR3 phenotype and lymphocyte responses to phytohaemagglutinin

Several reports have shown that HLA-B8,DR3 positive subjects may display some changes in immune parameters when compared with HLA-B8,DR3 negative ones and are prone to develop several immunological diseases. In the present study we have analysed the proliferative response to phytohaemagglutin (PHA) in HLA-typed healthy subjects. A twin method was also employed to assess the role of genetic and environmental factors in the regulation of the response to the mitogen. It was not possible to demonstrate any difference in proliferative response to optimal doses of PHA between groups of subjects carrying or not carrying the HLA-B8,DR3 phenotype. When suboptimal responses were studied, however, the results showed that lymphocyte responses were significantly decreased in HLA-B8,DR3 positive subjects compared with the negative ones. Moreover, the experiments performed with twins demonstrated that environmental factors were more important than genetic factors in the proliferative response to mitogen. The fact that the HLA-B8,DR3 phenotype affects the suboptimal response to PHA although environmental factors are more important than genetic factors in the response to the mitogen seems of some interest. However, these results could be consistent with the high incidence of autoimmune disorders among HLA-B8,DR3 positive individuals.

Lack of informative HLA restriction fragment length polymorphisms in autoimmune chronic active hepatitis

Autoimmune chronic active hepatitis (CAH) is strongly associated with HLA-B8, DR3. Accordingly, DNA was isolated from 10 HLA-B8, DR3 control subjects and 11 patients with autoimmune CAH and analyzed for informative restriction fragment length polymorphisms using HLA-DQ beta and DR beta probes, and six enzymes, Hinc II, Bgl II, Bam HI, Rsa I, Taq I and Msp I. None of the polymorphic fragments demonstrable was discriminatory for autoimmune CAH. A genetic polymorphism in the HLA-B8, DR3 region predisposing to autoimmune CAH may not have been detecting owing to an insufficient number of probes or enzymes used, or alternatively HLA-DR3 is predisposing by an effect on immune regulation or suppression.