The molecular structure of human antibodies specific for the human immunodeficiency virus

High frequency of virus-specific B lymphocytes in germinal centers of simian-human immunodeficiency virus-infected rhesus monkeys

The etiology of the lymphadenopathy and follicular hyperplasia associated with human immunodeficiency virus type 1 (HIV-1) infection has remained unclear. To determine whether the B-lymphocyte expansions characteristic of this syndrome represent polyclonal and virus-specific processes, the antigen specificity of B cells in lymphoid tissues of monkeys infected with simian-human immunodeficiency virus (SHIV) chimeras was assessed using an inverse immunohistochemical assay with biotinylated HIV-1 envelope gp120 (Env) as an antigen probe. Env-binding B cells were found aggregated in lymph node and splenic germinal centers (GCs). Most Env-binding GCs also contained an unstained population of B cells, suggesting the GCs were formed by a polyclonal (oligoclonal) process. By day 42 following infection, Env-binding B cells were present in 19% of all lymph node GCs. Env-binding cells were present in 25% of GCs even during chronic infection. This extraordinarily high frequency of Env-specific B lymphocytes suggests that the expansion of virus-specific B cells may largely account for the follicular hyperplasia in AIDS virus-infected individuals.

The Human Antibody Response to Porcine Xenoantigens Is Encoded by IGHV3-11 and IGHV3-74 IgVH Germline Progenitors

Preformed and induced Ab responses present a major immunological barrier to the use of pig organs for human xenotransplantation. We generated IgM and IgG gene libraries established from lymphocytes of patients treated with a bioartificial liver (BAL) containing pig hepatocytes and used these libraries to identify IgVH genes that encode human Ab responses to pig xenoantigens. Genes encoded by the VH3 family are increased in expression in patients following BAL treatment. cDNA libraries representing the VH3 gene family were generated, and the relative frequency of expression of genes used to encode the Ab response was determined at days 0, 10, and 21. Ig genes derived from the IGHV3-11 and IGHV3-74 germline progenitors increase in frequency post-BAL. The IGHV3-11 gene encodes 12% of VH3 cDNA clones expressed as IgM Abs at day 0 and 32.4–39.0% of cDNA clones encoding IgM Abs in two patients at day 10. IGHV3-11 and IGHV3-74 genes encoding IgM Abs in these patients are expressed without evidence of somatic mutation. By day 21, an isotype switch occurs and IGHV3-11 IgVH progenitors encode IgG Abs that demonstrate somatic mutation. We cloned these genes into a phagemid vector, expressed these clones as single-chain Abs, and demonstrated that the IGHV3-11 gene encodes Abs with the ability to bind to the gal α (1,3) gal epitope. Our results demonstrate that the xenoantibody response in humans is encoded by IgVH genes restricted to IGHV3-11 and IGHV3-74 germline progenitors. IgM Abs are expressed in germline configuration and IgG Abs demonstrate somatic mutations by day 21.

Antibody repertoire against HIV-1 gp120 triggered in nude and normal mice by GM-CSF/gp120 immunization

Granulocyte-macrophage colony stimulating factor (GM-CSF) facilitates the induction of primary immune responses by activating and recruiting antigen-presenting cells (APC), which efficiently present antigen determinants to Th cells. We have derived a functional GM-CSF/gp120 chimeric protein that, following immunization in soluble, adjuvant-independent form in normal mice, triggers highly specific, high affinity anti-gp120 antibodies. In contrast, nude mice respond with mutated, polyreactive, low affinity antibodies that mature further and increase in affinity in T cell-reconstituted nude mice. Anti-gp120 antibody production in nude mice is mediated principally by GM-CSF/gp120-triggered IL-4 production, since neutralizing anti-IL-4 abrogates the in vivo response. The anti-gp120 antibody response in normal, nude and T cell-reconstituted nude mice is encoded at a remarkably high frequency by the VH81X and VH7183 genes, a family used notably during fetal life and, when expressed at the adult stage, associated with autoimmune disease. We conclude that HIV gp120 binds and selects a subpopulation of developing B cells expressing a set of VH genes associated with immunodeficiency and autoimmunity.

Clonal Analysis of a Human Antibody Response. III. Nucleotide Sequences of Monoclonal IgM, IgG, and IgA to Rabies Virus Reveal Restricted Vκ Gene Utilization, Junctional VκJκ and VλJλ Diversity, and Somatic Hypermutation

In previous work, we generated four IgM, five IgG1, and one IgA1 mAbs to rabies virus using B cells from four subjects vaccinated with inactivated rabies virus, a thymus-dependent (TD) mosaic Ag, and sequenced the mAb VHDJH genes. Here, we have cloned the VκJκ and VλJλ genes to complete the primary structure of the Ag-binding site of these mAbs. While the anti-rabies virus mAb selection of Vλ genes (2e.2.2 twice, DPL11, and DPL23) reflected the representation of the Vλ genes in the human haploid genome (stochastic utilization), that of Vκ genes (O2/O12 twice, O8/O18, A3/A19, A27, and L2) did not (p = 0.0018) (nonstochastic utilization). Furthermore, the selection of both Vκ and Vλ genes by the anti-rabies virus mAbs vastly overlapped with that of 557 assorted VκJκ rearrangements, that of 253 VλJλ rearrangements in λ-type gammopathies, and that of other Abs to thymus-dependent Ags, including 23 anti-HIV mAbs and 51 rheumatoid factors, but differed from that of 43 Abs to Haemophilus influenzae type b polysaccharide, a prototypic thymus-independent (TI) Ag. The anti-rabies virus mAb VκJκ and VλJλ segments displayed variable numbers of somatic mutations, which, in mAb58 and the virus-neutralizing mAb57, entailed a significant concentration of amino acid replacements in the complementarity-determining regions (p = 0.0028 and p = 0.0023, respectively), suggesting a selection by Ag. This Ag-dependent somatic selection process was superimposed on a somatic diversification process that occurred at the stage of B cell receptor for Ag rearrangement, and that entailed V gene 3′ truncation and N nucleotide additions to yield heterogeneous CDR3s.

Immunoglobulin V(H) usage during primary infection of rhesus monkeys with chimeric simian-human immunodeficiency viruses

It has been suggested that naive immunoglobulins encoded by the V(H)3 gene family interact aberrantly with human immunodeficiency virus type 1 (HIV-1) gp120 via a superantigenic epitope, causing initial expansion and eventual depletion of V(H)3-expressing B cells. However, this possibility has not been prospectively assessed during an AIDS virus infection. We determined V(H) family usage in rhesus monkeys during primary infection with chimeric viruses expressing HIV-1 envelopes on a simian immunodeficiency virus (SIVmac) backbone (SHIVs). Four SHIVs with different envelopes and pathogenicities were studied. V(H) family usage was prospectively assessed in peripheral blood mononuclear cells and lymph node cells of these monkeys by a semiquantitative PCR technique. In the first months following SHIV infection, a period of intense viral antigenemia, representation of various V(H) families increased or decreased for individual monkeys, but no single V(H) family was consistently altered. In particular, the average representation of V(H)3-bearing B lymphocytes did not change. This observation suggests that the envelope glycoprotein of HIV-1 does not selectively expand or deplete the V(H)3 repertoire of primate B cells during acute AIDS virus infection, contrary to predictions of the gp120 superantigen hypothesis.

B cell superantigens in HIV-1 infection

HIV-I infection affects many of the cellular components vital for the maintenance of immune homeostasis. Similar to the T cell superantigen effect on T cell expansion and depletion in AIDS. HIV components with B cell superantigenic properties could be responsible for the observed B cell activation and skewing of VH family usage. Current data on possible B cell superantigen properties of HIV proteins (gp120) are mostly based on studies describing the clonality and VH family usage of immunoglobulins in HIV infection. Various laboratories reported independently an unusual skewing of the VH-repertoire of antibodies that appears not to be random. According to these observations, an enrichment of VH1 and VH4 family-paralleled a depletion of VH3 family-utilizing anti-HIV-1 gp120 and p24 antibodies in HIV-1 infected individuals and a loss of total VH3+ Ig in patients with late stages of AIDS. Polyclonal and monoclonal (VH1, VH4, and VH5) anti-p24 and gp120 antibodies share a crossreactive idiotype (IF7). IF7 like antibodies were found in the serum of HIV-1 infected individuals, persisting in the course of infection, perhaps contributing to the depletion of VH3 Ig. Furthermore a restriction of clonal heterogeneity of anti-p24 and anti-gp120 antibodies was detected by isoelectric focusing and indicated by skewed kappa/lambda light chain isotype ratios, indicating clonal dominance of certain sets of anti-HIV-1 antibodies during infection. Taken these findings together, a strong case for the involvement of a B cell superantigen can be made, although the mechanism of B cell depletion is not fully understood.