Antibodies to immunoglobulin heavy chain variable regions protect helper cells from specific suicide by radiolabeled antigen

Monoclonal anti-VH antibodies recognize a common VH determinant expressed on immunoglobulin heavy chains from various species

Our previous work using rabbit antibodies to the variable region of MOPC315 myeloma heavy chain (VH) has indicated the existence of framework determinant(s) common to many murine heavy chains. Here we report the characterization of anti-VH monoclonal antibodies (mAb) prepared in an attempt to elucidate the nature of the common VH determinant. We immunized AKR/J mice with a purified VH315 fragment and generated somatic cell hybrids by the fusion of the immune AKR/J splenocytes with the NS1 myeloma cells. Thirty-seven common anti-VH and 57 subgroup VHI-specific hybridomas have been established and characterized. Whereas the anti-subgroup mAb seemed to react with a determinant unique to the MOPC315 (mouse VHI) subgroup, all the anti-VH mAb reacted with myeloma heavy chains of different VH subgroups, class and allotypes. Antibody competition studies revealed that the VH subgroup determinants are distinct from the common VH determinants and that both were also recognized by the rabbit polyclonal antibodies. The common VH determinants were found to be "hidden" determinants on intact immunoglobulin molecules being exposed only on isolated heavy chains. Furthermore, they are sequential determinants since they are preserved on fully denatured heavy chains. The common VH determinants are shared by immunoglobulins of a wide range of vertebrates from amphibia to man and thus represent antigenic structures which were highly conserved throughout evolution.

Use of somatic cell genetics to study chromosomes contributing to antigen plus I recognition by T cell hybridomas

Keyhole limpet hemocyanin (KLH)/I region-specific T cell hybridomas have been prepared by fusing KLH/I-specific T cell blasts from mice with single pairs of metacentric chromosomes to the inducible, interleukin 2 (IL-2)-secreting T cell hybridoma FS6-14.13.AG2.1. T cell hybridomas with KLH/I receptors were identified by their ability to secrete IL-2 in response to KLH and the appropriate antigen-presenting cells. After cloning and subcloning, KLH/I reactivity was correlated with the presence or absence of metacentric chromosomes derived from the KLH/I-specific T cell blast parent. Hybridomas were identified that had lost all chromosomes 4 and 6 or 16 and 17 derived from their normal T cell parent, but retained the ability to respond to KLH/I. This suggested that products of genes on these chromosomes did not contribute to the specific portions of T cell Ag/I receptors. These gene products would include, of course, kappa and lambda chains and H-2. We did not obtain any T cell hybridomas that had lost both metacentric (8.12) chromosomes derived from T cells of the Robertsonian mouse strain Rb(8.12)5, so we could not draw any conclusions about the contributions of products of genes on these chromosomes. T cell hybridomas with KLH/I reactivity were found that contained only one metacentric (8.12) chromosome derived from this strain. Moreover, a T cell hybridoma was found that retained both metacentric (8.12) chromosomes from its normal T cell parent, but had lost KLH/I reactivity. These results suggested that neither two chromosomes 8 nor two chromosomes 12 were required for antigen/I reactivity in normal T cells and that antigen/I reactivity was controlled, at least in part, by genes mapping on chromosomes other than 8 or 12.

A monoclonal antibody against antigen-specific helper factor augments T-cell help

Antigen-specific molecules, commonly termed 'factors', have been shown to be released from helper and suppressor T cells. These factors mimic the activity of the cells that secrete them and there is much speculation about the relationship of antigen-specific factors to T-cell receptors for antigen. We have raised a variety of antisera in rabbits which were shown to react against conserved 'constant' determinants on either helper or suppressor factors independently of antigenic specificity or mouse strain of origin of the factor. In contrast, syngeneic mouse antisera were found to react with 'variable' factor determinants in an antigen-specific and mouse strain-dependent manner. These antisera thus define two regions on factor molecules, one 'variable' (related to antigen specificity) and the other 'constant' (related to function). However, potential contaminants in these antisera have limited their usefulness. Thus, we are now generating monoclonal antibodies against T-cell factors and report here the properties of a monoclonal antibody (AF3.44.4) which reacts with antigen-specific helper factors. This antibody also binds to helper T cells and, in the presence of antigen, augments helper cell induction in vitro, which, in turn, leads to enhanced antibody production in vitro. These characteristics suggest that AF3.44.4 recognizes a determinant shared by helper factor and the antigen receptor on helper T cells.

Effects of anti-Ig reagents on T cell functions I. Activation of rabbit T cells by anti-allotype antibodies

Rabbit lymphocytes were analyzed by flow microfluorometry, using anti-T cell and anti-Ig reagents. Rabbit T cells and cells expressing surface Ig (B cells) appeared to belong to distinct subpopulations which could be separated on the basis of their selective adherence to nylon wool columns or to anti-Ig-coated dishes. Using flow microfluorometry, no evidence was obtained for the expression of a allotypes (VH framework) on T cells. Separated lymphocyte populations were functionally characterized using an in vitro proliferation assay. B and T cells from rabbit spleen or peripheral blood responded in a differential fashion to B and T cell-specific mitogens and to anti-Ig antibodies. Although such T cells did not respond upon stimulation with anti-Ig antibodies alone, significant proliferation could be induced by simultaneous addition of anti-Ig and T cell growth factor. In addition, activated T cells, derived from lymph nodes of immunized rabbits, generated a proliferative response upon stimulation with anti-Ig reagents alone. The above-mentioned effects on T cells could be obtained using heterologous anti-Ig antibodies or isologous anti-allotype antibodies, directed either against a allotypes (VH framework) or against b allotypes (kappa light chain). Antibodies against the Fc portion of rabbit Ig or against irrelevant allotypic specificities were ineffective in triggering T cells. Fab fragments from anti-allotype antibodies were equally stimulatory for T cells as compared to intact IgG, indicating that cross-linking of Ig-like molecules is not a necessary requirement for anti-Ig-induced T cell activation.

Immunoglobulin VH determinants defined by monoclonal antibodies

Hybridoma clones secreting antibodies against common VH determinants were readily produced by fusion of cells from mice immunized with isolated V mu fragments of human immunoglobulins (Ig), but not with intact Ig molecules or isolated heavy chains. Four monoclonal antibodies to the V mu fragments of different IgM paraproteins were selected for analysis: MH-44 (mu kappa), GB-24 (mu kappa), NF-11 (gamma 1 kappa), and SA-44 (gamma 1 kappa). Each antibody reacted with the homologous V mu fragment, homologous mu chain, and normal gamma chains, but not with the intact IgM molecules, intact IgG, or isolated light chains, as determined by radioimmunoassay. The VH reaction spectra with a panel of myeloma heavy chains showed overlapping but distinctive patterns for the four antibodies. Each of the four monoclonal anti-VH antibodies appeared to react with a different "hidden" VH determinant that is not exposed on undenatured, intact Ig molecules and differs from conventional VH subgroup determinants. In immunofluorescence studies, the monoclonal anti-VH antibodies did not bind to surface Ig on viable B lymphocytes, but visibly stained subpopulations of fixed B lymphocytes, pre-B cells, and normal plasma cells. The mean frequencies of VH+ plasma cells were 30% (MH-44), 17% (GB-24), 13% (NF-11), and 3% (SA-44), and similar frequencies were obtained for the VH+ B cell subpopulations. While subpopulations of B cells could be identified at all stages in differentiation by immunofluorescence with the anti-VH antibodies, neither resting nor activated T cells expressed these VH determinants in detectable amounts.

Two separate genes regulate self-Ia and carrier recognition in H-2-restricted helper factors secreted by hybridoma cells

H-2 heterologous T cell hybridomas were used to study the genetic control of dual, anti-nominal antigen and anti-self H-2 specificity of H-2 restricted T cell factors. Each of four hybridoma clones produced two helper factors. One was restricted for the Ia type of the normal T cell partner (H-2b), whereas the other was restricted for the ia type of the lymphoma partner (H-2k) of the somatic hybrid. This was shown by affinity separation on parental type spleen cells and on monoclonal anti-I-A-Sepharose. Both factors had carrier (chicken gamma globulin; CGG)-specific helper effect, and both bound to anti-VH-315-Sepharose. Because the lymphoma (BW-5147) partner could not contribute a CGG-specific locus, the H-2k-restricted, CGG-specific factor had to be the product of segregating anti-nominal and anti-self loci. This suggests that dual specificity is due to two independent loci and support the validity of dual recognition concepts. Anti-self specificity was associated with homologous Ia alloantigens in the individual factors. Therefore, Ia and anti-self might be linked. Implications of the major histocompatibility complex or VH nature of anti-self receptors and the relationship of T cell factors and receptors was discussed.

Defective induction of antigen-reactive proliferating T cells in B cell-deprived mice

Mice were injected from day of birth onward with rabbit anti-mouse IgM antiserum or purified rabbit anti-mouse IgM antibodies. These mice completely lacked Ig-positive cells or serum Ig, as analyzed by specific fluoresceinated antibodies on the fluorescence-activated cell sorter (FACS-II), by polyclonal B cell mitogens and by specific precipitation in agar. These animals were then primed in vivo by antigen emulsified in complete Freund's adjuvant, and, subsequently, their draining lymph nodes were tested for their T cell proliferative responses in vitro, to the relevant antigen and were found to be severely impaired. However, the antigen-presenting capacity of both spleen cells and thioglycollate-induced peritoneal cells was found to be intact.

H-2-restricted helper factor secreted by clone hybridoma cells

Biological and serological characteristics of a helper factor secreted by cloned hybridoma cells was described. The factor is carrier specific and contains determinants shared with immunoglobulin VH bu does not react with V kappa- or V lambda-specific antibodies. Presence of four H-2I-controlled antigenic specificities, Ia.ml, Ia.m2, Ia.17, and Ia.m7, was detected. Hence, it is possible that both A beta and E alpha loci may be involved in its control. Helper effect could be obtained only toward B cell sources that shared the H-2K and I-A antigens with the hybridoma cells. Similarly, the factor was absorbed only by spleen cells syngeneic in I-A. Previous studies have demonstrated that this clone binds antigen in an H-2-restricted manner. It follows that H-2-restricted helper cells produce H-2-restricted helper factors. Hence, they support the view that specific T cell factors may represent secreted T cell receptors.

H-2-restricted antigen binding by a hybridoma clone that produces antigen-specific helper factor

Somatic cell hybrids were prepared by fusing the AKR mouse lymphoma BW-5147 with splenic T cells from mice immunized with 4-hydroxy-3-nitrophenylacetic acid (NP) conjugated to chicken serum globulin (CG). From 500 fusion lines 11 were selected on the basis of binding radioiodinated NP-CG. The autoradiographic binding assay was based on previous findings which showed that Lyt-1+ T cells need a lymphokine, lymphocyte-activating factor (LAF), for optimal antigen binding and that they bind preferentially a self-Ia-associated antigen complex, IAC, which is released by adherent cells upon incubation with antigen. Six of the 11 antigen-binding positive lines were tested for helper activity and specific helper factor production in vitro. All of them were found to be positive. One clone was characterized in more detail. It secretes a CG-specific helper factor that contains immunoglobulin heavy chain variable region and I-A determinants. The hybridoma cells bind Ia-containing CG complexes specifically. For binding they need to be treated with LAF, and the binding is restricted to syngenicity in H-2 between the adherent cells used to produce IAC and the antigen-binding hybridoma cells. Regular CG does not bind significantly and does not compete even at high excess with the binding of CG-IAC. These data are interpreted to suggest that the antigen is bound by cells of a clone functional helper T-cell hybridoma line in conjunction with products controlled by H-2I and that the receptor of these cells may have considerably higher affinity for Ia-associated than for regular antigen.