Antibody-dependent cell-mediated cytotoxicity against cells infected with the human immunodeficiency virus.

Human immunodeficiency virus (HIV) elicits the production of virus-specific antibodies in infected individuals. We investigated the ability of serum from HIV-infected individuals to mediate antibody-dependent cellular cytotoxicity in an in vitro 51Cr release assay system. Fresh peripheral blood mononuclear cells from healthy donors seronegative for HIV were used as cellular effectors against HIV-infected and uninfected H9 target cells in the presence of serum from HIV-infected or uninfected donors. Serum from HIV-infected, but not uninfected, donors significantly augmented cytolysis of virus-infected targets (P less than .005). There was no augmented killing of uninfected H9 cells with sera from either group. Studies using serum from mice that had been immunized with synthetic peptides from the HIV envelope region suggested that this response is directed, at least in part, at several determinants of the transmembrane portion of the HIV envelope glycoprotein.

Human immunodeficiency virus neutralizing antibodies recognize several conserved domains on the envelope glycoproteins.

Serum neutralizing antibodies against the human immunodeficiency virus were frequently detected in infected individuals, and low or absent serum neutralizing titers correlated with poor prognosis. Multiple diverse human immunodeficiency virus isolates were found to exhibit similar susceptibility to neutralization by a panel of human seropositive sera, suggesting that neutralizing antibodies are largely directed against conserved viral domains. Furthermore, utilizing antisera raised against a library of synthetic env peptides, four regions which are important in the neutralization process have been identified within both human immunodeficiency virus envelope glycoproteins (gp41 and gp120). Three of these are in conserved domains and should be considered for inclusion in a candidate vaccine.

Variable region sequences of murine IgM anti-IgG monoclonal autoantibodies (rheumatoid factors). A structural explanation for the high frequency of IgM anti-IgG B cells.

The nucleotide sequences of heavy and light chains from 10 monoclonal IgM anti-IgG1 (RF) antibodies were determined and reported here as translated amino acid sequences. Only three families of VK light chains were used in these antibodies: VK1 (two examples), VK8 (three examples), and VK19 (four examples). This represents a significant nonrandom selection of light chains. In contrast, all other variable region gene segments (i.e., VH, DH, JH, and JK) were used in a pattern consistent with random selection from the available pool of germline genes. In two cases, the same anti-IgG1 specificity was generated by a combination of very homologous light chains with unrelated heavy chains. We infer from this that the light chain is the segment used by these antibodies to bind IgG1. The nature of these sequences provides an explanation for the curious observation that as many as 15% of splenic B cells in normal mice may be expressing IgM anti-IgG; if, as our data suggest, certain light chains in combination with many different heavy chains can be used in assembling the anti-IgG specificity, then, because of combinatorial association in which the heavy chain is not relevant for specificity, the fraction of IgM-producing B cells expressing these light chains should approximate the fraction of B cells making IgM anti-IgG. We calculate, based on data presented in several other studies, that 5-17% of B cells express one of the VK types observed in monoclonal RF. This agrees well with estimates for the number of B cells making IgM anti-IgG. In addition, our findings could rule out other explanations of the high percentage of B cells making RF, such as constant stimulation by antigen or presence of numerous antigenic epitopes since it was shown that IgM anti-IgG1 antibodies are not somatically mutated and that they are structurally homogeneous. We aligned the VK sequences of the RF in hopes of finding some primary sequence homology between the represented VK families which might point to residues involved in the binding interaction. Although we found no such homology in the hypervariable regions, we did find significant and unexpected homology in the FR2 and FR3 of these light chains. We noted that these regions are exposed in the Ig structure and postulate that they may be involved in a unique type of binding interaction between two Ig family domains, i.e., VK binding to a constant region domain of IgG.

Combinational diversity within variable regions bearing the predominant anti-p-azophenylarsonate idiotype of strain A mice.

The humoral immune response in strain A mice to protein conjugates of p-azophenylarsonate (Ars) is characterized by the presence of a major cross-reactive idiotype denoted as IdCR. Previous molecular analyses of monoclonal IdCR+ Ars-binding antibodies isolated from multiply immunized animals have indicated that these antibody variable (V) regions may be the expressed product of a single combination of VH, D, JH, V kappa, and J kappa gene segments. The basis of this apparent domination of the Ars response by V regions encoded by this single combination of gene segments is unclear, but is discussed in this report. Our structural analyses on five monoclonal IdCR+ antibodies that are unable to bind Ars show that in contrast to those of Ars-binding IdCR+ antibodies, these (Ars-nonbinding) IdCR+ V regions are encoded by multiple combinations of VH, D, JH, V kappa, and J kappa gene segments, but with the commonality that they all utilize a single VH gene segment (VHIdCR). We provide examples in which the VHIdCR gene segment is expressed with three different V kappa gene segments and with each of the four JH gene segments to produce serologically detectable IdCR+ Ars-nonbinding antibodies. It would thus appear that the previous failure to detect alternative IdCR+ V segment combinations was due to a sampling procedure requiring that the IdCR+ antibody bind Ars, and not the result of restricted assembly or expression of the VHIdCR gene segment with a particular combination of D, JH, V kappa, and J kappa gene segments. This bias in protocol, however, cannot completely account for the homogeneity in previously studied IdCR+ Ars-binding antibodies, because we were able to isolate, from primary immune responses, IdCR+ antibodies that do bind Ars but that utilize alternative V segment combinations. This finding suggests that combinations of V gene segments encoding IdCR+ antibodies are more numerous in primary as opposed to secondary immune responses, and raises the question of why a single combination of VH, D, JH, V kappa, and J kappa gene segments dominates the secondary strain A immune response to Ars.

Induction of rheumatoid antibodies in the mouse. Regulated production of autoantibody in the secondary humoral response.

A/J mice were found to produce autoreactive IgM anti-IgG1 in response to secondary immunization with a number of protein antigens. No anti-IgG1 was produced after a single such immunization, indicating that antigen: IgG1 antibody complexes were responsible for inducing the autoreactive response. The size of the anti-IgG1 response was in some cases massive and of the same order of magnitude as the response to the foreign immunizing material. No significant anti-IgG2a, anti-IgG2b, or anti-IgG3 response was found in mice producing anti-IgG1. Virtually all of the anti-IgG1 material produced was of the IgM class and bound to the Fc region of autologous IgG1. A component of the anti-IgG1 was shown to be able to distinguish between the two mouse IgG1 allotypes. These results suggest that self-reactive anti-IgG is a common component of the secondary immune response of mice that may have powerful physiological and immunoregulatory effects.

Immunoglobulin idiotype and anti-anti-idiotype utilize the same variable region genes irrespective of antigen specificity.

Idiotypic determinants characterizing certain antibody specificities have been proven valuable structural and genetic markers in studies of antibody diversity and regulation. The heritable predominant idiotype associated with the response to p-azophenylarsonate in A/J mice consists of a set of highly homologous (greater than 95%) heavy and light chain variable region amino acid sequences probably arising by somatic mutation from one or a few V region genes. We examined a peculiar set of monoclonal antibodies that have been defined as CRI by serologic analysis, but that have no affinity for the hapten Ars. These antibodies were elicited by immunization with anti-CRI rather than by the conventional immunization with antigen. The amino acid sequences of the amino terminal half of the V regions of these anti-(anti-CRI) antibodies are indistinguishable from those of conventional Ars-binding CRI antibodies. Thus, Ars-binding CRI and Ars-nonbinding anti-(anti-CRI) are derived from similar or identical VH and VL genes.

Differentiation and activation of nu/nu splenic T cell precursors by mature peripheral T cells in the absence of thymus.

Nu/nu splenic T cell precursors lacking significant Thy-1 surface antigen are driven in vitro to proliferate and express Thy-1 during incubation with activated, nondividing peripheral T cells in the absence of thymus or thymic extracts. The precursors are present in nu/+ spleen as well, and are phenotypically similar to thymocyte precursors assayed in vivo. The nondividing inducer cells required are Lyt-2-, Thy-1+ T cells present in nu/+ but not nu/nu spleen and show no MHC restriction in the induction process. Using this in vitro assay, we preliminarily identified a monoclonal rat anti-mouse brain antibody that lyses nu/nu responding T cell presursors in the presence of complement. The ability of mature peripheral T cells to induce the differentiation and activation of T cell precursors in the complete absence of thymus appears to explain the grossly different effects of neonatal and adult thymectomy or thymic involution on immunocompetence. In addition, we showed that the limiting cell in three-cell mitogenic response of normal spleen cells to Con A is likely the macrophage by similar analysis of nondividing inducer cell requirements. This finding allows the assignment of a unique order to this three-cell response.

Enhancing antibody: a novel component of the immune response.

Current descriptions of the immune response identify two classes of antigenic stimuli that result in the production of specific antibody: (i) exogenous antigens and (ii) endogenous variable-region determinants of the immune system. We expand this scheme to include a third class of antigenic stimulus--new determinants created by the binding of antibody to antigen. This paper describes a set of monoclonal antibodies which arose after repeated immunization with antigen alone but which bound antibody--antigen complexes. These antibodies recognize determinants on the antibody portion of the complexes that were expressed as a consequence of antigen binding. Antibodies of this general type, "enhancing antibodies," which can strengthen antibody--antigen and idiotypic-anti-idiotypic antibody interactions, may play important regulatory and effector roles in the immune response. We suggest a model that predicts the occurrence and specificity of different classes of such antibodies and provides a conceptual framework that gives a straightforward explanation of the appearance in the immune response of rheumatoid antibodies and of antibodies that bind cooperatively to antigen.

The strain A anti-p-azophenylarsonate major cross-reactive idiotypic family includes members with no reactivity toward p-azophenylarsonate.

The sera of immunized A/J mice contain low but detectable levels of immunoglobulin, bearing previously described cross-reactive idiotypic (CRI) determinants diagnostic of the strain A anti-p-azophenylarsonate (Ars) response. Such molecules from nonimmune sera cannot be adsorbed onto affinity columns coupled to a high density with Ars. After extensive immunization with Ars-coupled proteins, Ars-nonbinding CRI is found at the same low level, even though substantial Ars-binding CRI appears. On the other hand, immunization with a monoclonal rat anti-CRI, which was originally raised against Ars-binding CRI, elicits high concentrations of Ars-binding as well as Ars-nonbinding CRI immunoglobulin. Three hybridoma proteins produced from an A/J mouse immunized with the rat anti-CRI react with all tested anti-idiotypic sera from three species of animals, but show no reactivity toward Ars in several different assays. One hybridoma protein from the same fusion demonstrates Ars-binding capacity.

Monoclonal antibodies against a specific nonhistone chromosomal protein of Drosophila associated with active genes.

Hybridomas secreting monoclonal antibodies have been produced by fusion of NS-1 mouse myeloma cells with the spleen cells of mice inoculated with a 60-65,000-mol wt fraction of proteins released from Drosophila embryo nuclei treated with DNase I. The antibodies secreted by the hybridomas were examined with polytene chromosomes of formaldehyde-fixed salivary gland squashes by an immunofluorescence assay. Most of the clonal antibodies obtained resulted in specific staining of the chromosomes relative to the cytoplasmic debris. In the case of clone 28, the antibodies showed a preferential association with sites of gene activity, both puffs and loci identified as puffing at some time during the third instar and prepupal period. In larvae that were heat shocked (exposed to 35 degrees C for 15 min before removal and fixation of the glands), the antibodies of clone 28 stained preferentially the induced heat-shock loci while continuing to stain most of the normal set of loci. The antigen for clone 28 was identified as a single protein of approximately 62,000 mol wt by using the antibodies followed by 125I-rabbit anti-mouse Ig to stain nitrocellulose replicas of SDS polyacrylamide gels of total chromosomal proteins. This study demonstrates that monoclonal antibodies can be used successfully in immunofluorescence staining of formaldehyde-fixed polytene chromosomes. The results verify the hypothesis that a specific nonhistone chromosomal protein is preferentially associated with the set of loci that includes both active sites and those scheduled to be active at some time in this developmental program. Such proteins may play a general role in the mechanisms of cell determination and gene activation.

Precursors of murine B lymphocytes. Physical and functional characterization, and distinctions from myeloid stem cells.

The emergence of functional B cells was monitored in irradiated or unirradiated CBA/N recipients of either adult bone marrow or fetal liver from CBA/HT6T6 donors. The cells that are primarily responsible for the generation of B lymphocytes, at least during the first 6 wk, are rapidly sedimenting (4.5-6 mm/h), lack surface immunoglobulin, and are found in both the adult bone marrow and the fetal liver from day 12 onward. These pre-B cells are distinct from the colony-forming unit spleen (CFU-s) as demonstrated by the following criteria: (a) absence from yolk sac (19), (b) lack of correlation between CFU-s number and the ability to generate B cells in fetal liver populations of different ages of gestation, and (c) hybridoma antibodies that significantly inhibited B cell reconstitution but have no effect on CFU-s numbers. The antigen detected by this antiserum is present on both the fetal liver and bone marrow B cell progenitor, although its expression is not restricted to the B lineage. The pre-B cells that we monitor are not homogeneous, however, as both physical and functional differences are found. These observations reinforce our thesis that committed progenitor cells for the humoral immune system are formed early in development and thereafter constitute the major precursor pool for the generation of B lymphocytes.

Monoclonal rat anti-mouse brain antibody detects Abelson murine leukemia virus target cells in mouse bone marrow.

We report the characterization of a monoclonal antibody which detects a surface antigen expressed by the bone marrow target cell of A-MuLV. Treatment of bone marrow cells with this antibody and complement results in greater than loss 95% loss of the A-MuLV-derived in vitro transformed foci. The surface antigen detected by this antibody is also expressed on A-MuLV-transformed lymphoid cell lines, thymocytes, and some peripheral lymphocytes. This antigen is not expressed, however, by the pluripotent hematopoietic stem cell defined by the spleen colony-forming assay. We present evidence that the antigen detected is neither a virally encoded product, nor exclusively associated with the BALB/c genome.

"Panning" for lymphocytes: a method for cell selection.

We have developed a simple method for the fractionation of T and B lymphocytes. Plastic dishes coated with antibodies specific for mouse Ig selectively bind splenic B lymphocytes. The adherent cells are easily removed by gentle pipetting; both adherent and nonadherent populations retain immunologic function. In a typical experiment, when 3 X 10(7) splenic lymphocytes were added to a 100 X 15 mm plastic dish coated with microgram quantities of anti-Ig, 98 % of the nonadherent cells were Ig negative and 97% of the adherent cells were Ig positive. The method is sufficiently sensitive to allow detection and separation of cell types comprising as little as 2% of the total population and can be modified to allow the selection of cells by a double-antibody procedure. We believe that the plastic dish method will be generally useful for fractionating cells on the basis of their cell surface antigens.

T-cell regulation of antibody responses: demonstration of allotype-specific helper T cells and their specific removal by suppressor T cells.

Allotype suppressor T cells (Ts) generated in SJL X BALB/c mice specifically suppress production of antibodies marked with the Ig-1a allotype. The studies presented here show that allotypes Ts suppress by specifically removing helper T cell (Th) activity required to facilitate differentiation and expansion of B cells to Ig-1b antibody-forming cells. We show first that Ts and Th belong to different T-cell subclasses as defined by Ly surface antigens. Ts are Ly2+Lyl- and thus belong to the same subclass as cytotoxic precursor and effector cells; Th are Lyl+Ly2- cells and thus belong to the subclass containing cells which can exert helper functions and initiate delayed hypersensitivity reactions. Placing these cells in these two subclasses shows that Th are different from Ts and suggests that they play different roles in regulating antibody responses. The difference in these roles is defined by the evidence presented here showing that Ts attack Th and regulate the antibody response by specifically regulating the availability of Th activity. We show that in allotype suppressed mice, Ts which suppress Ig-1b antibody production have completely removed the Th activity of helping Ig-1b cells without impairing Th activity which helps other IgB B cells. These findings imply the existence of allotype-specific Th for Ig-1b cells (Ig-1b Th). We directly establish that Ig-1b cells require such help by showing that carrier-primed spleen cells from Iga/Iga congenic hybrids help Ig-1a B cells from hapten-primed Igb/Iga donors but do not help Ig-1b B cells from the same donor in the same adoptive recipient.