Modification of T cell antinuclease idiotype expression by in vivo administration of anti-idiotype

Immunization of BALB/c mice with nuclease leads to the production of anti-nuclease antibodies bearing a set of cross-reactive idiotypes (Id) distinct from those produced by B10.D2 mice after similar immunization. In both strains, such immunization with nuclease also leads to the production of splenic T helper cells (TH), which provide nuclease-specific help in an in vitro plaque-forming cell response to nuclease-TNP. Pig anti-(BALB/c antinuclease) anti-idiotypic antibodies (pig anti-BALB/c Id) react only with TH of nuclease-primed BALB/c and not with B10.D2 animals. After administration of pig anti-BALB/c Id in complete Freund's adjuvant to BALB/c and B10.D2 mice, Id-bearing nonantigen-binding molecules were induced in both strains. Such treatment also resulted in the induction of nuclease-specific splenic TH cells in both strains. BALB/c TH cells induced by anti-Id, like the majority of nuclease-primed BALB/c TH cells, bore BALB/c Id, as shown by their functional elimination with anti-Id plus complement. B10.D2 TH cells induced by anti-Id, unlike TH cells from nuclease-primed B10.D2 mice, also bore BALB/c idiotypic determinants by the same criterion. Thus, it appears that one can manipulate the expression of Id on serum immunoglobulins and on antigen-specific TH cells by administration of exogenous anti-Id reagents. These results have implications both for network interactions in the immune response and for the genetic basis of Igh-C linked Id expression.

T cells from fully H-2 allogeneic (A replaced by B) radiation bone marrow chimeras are functionally competent and host restricted but are alloreactive against hybrid Ia determinants expressed on (A x B)F1 cells

In this communication it is demonstrated that T cells from fully allogeneic A replaced by B radiation bone marrow chimeras are alloreactive against the hybrid Ia molecules expressed on the surface of heterozygous A X B cells. These results suggested that previous failures to generate cytotoxic T lymphocyte (CTL) responses from fully allogeneic chimeras by sensitizing the chimeric T cells to antigen in an (A X B)F1-priming environment might have been confounded by an ongoing alloreaction against determinants created by hybrid Ia molecules expressed on F1 cells. Consequently, the ability to generate CTL responses from fully allogeneic chimeras was re-examined by sensitizing the chimeric T cells to antigen presented by homozygous rather that F1 stimulator cells. It was found that T cells of donor bone marrow origin that mediate cytotoxic responses to trinitrophenyl-modified self determinants do differentiate into functional competence in an H-2-incompatible host environment and are restricted to the host H-2 haplotype.

Major histocompatibility complex-restricted self-recognition in responses to trinitrophenyl-Ficoll. A novel cell interaction pathway requiring self-recognition of accessory cell H-2 determinants by both T cells and B cells

In vitro primary antibody responses to limiting concentrations of trinitrophenyl (TNP)-Ficoll were shown to be T cell dependent, requiring the cooperation of T helper (TH) cells, B cells, and accessory cells. Under these conditions, TH cells derived from long-term radiation bone marrow chimeras were major histocompatibility complex (MHC) restricted in their ability to cooperate with accessory cells expressing host-type MHC determinants. The requirement for MHC-restricted self-recognition by TNP-Ficoll-reactive B cells was assessed under these T-dependent conditions. In the presence of competent TH cells, chimeric B cells were found to be MHC restricted, cooperating only with accessory cells that expressed host-type MHC products. In contrast, the soluble products of certain monoclonal T cell lines were able to directly activate B cells in response to TNP-Ficoll, bypassing any requirement for MHC-restricted self-recognition. These findings demonstrate the existence of a novel cell interaction pathway in which B cells as well as TH cells are each required to recognize self-MHC determinants on accessory cells, but are not required to recognize each other. They further demonstrate that the requirement for self-recognition by B cells may be bypassed in certain T-dependent activation pathways.

Genetic analysis of the Mls system. Formal Mls typing of the commonly used inbred strains

In order to elucidate the biological role of minor lymphocyte stimulating (Mls) gene products, we have been investigating the fundamental immunogenetic characteristics of the Mls system. In this report, we describe the distribution of stimulatory Mls products, Mlsa and Mlsc, in a panel of laboratory inbred strains based on the response pattern of H-2-compatible naive T-cell populations as well as monospecific Mlsa- or Mlsc-reactive T-cell clones. In addition, the expression of four different T-cell receptor (Tcr) b-V segment Tcrb-V3, -V6, -V8.1, and -V9, which were recently reported to be associated with T-cell recognition of Mls gene products in these strains, was examined. The results indicate that the majority of commonly used laboratory strains including those originally typed as Mlsa are also expressing Mlsc determinants and that very few independent inbred strains are non-Mlsc. Moreover, the pattern of Tcrb-V expression in spleen as well as in thymus suggests that the association between Mls expression and clonal deletion of self Mls-reactive T cells appears to be the general rule in inbred strains. Based on these results, implications for the nondetectable Mls-like gene products in other species besides the mouse are discussed.

The National Institute on Aging at its twentieth anniversary: achievements and promise of research on aging

As these distinguished speakers demonstrate, the research community should take enormous pride in its many achievements to date, as well as in the scientific break-throughs that appear to be just on the horizon. However, existing gaps in our knowledge about the aging process certainly will require a great deal more of our attention. As former NIA director Robert N. Butler, MD, cautioned in the symposium's opening panel, "We remain ill-prepared for the 21st Century when population aging will become unprecedented. We already feel the impact of a revolution in longevity that has added 28 years to the life expectancy of Americans since the beginning the century. But we are not prepared for the baby boomers--the largest generation in U.S. history and one-third of our present population, the first of whom will turn 65 in 2011. "I regard the baby boomers as a generation at risk. We still devote relatively few resources to understanding the biology of aging. Although we have made progress in understanding the pathogenesis of Alzheimer's disease, we are a long way from a cure. While we have some insights into the demography of aging, the social impact of population aging upon society and, in turn, the psychosocial experiences of growing older, we are a long way from understanding the full implications of any of these." Maintaining and improving the health and well-being of older people will be among the greatest social challenges of the next century. Research into aging and the diseases common to older people undoubtedly holds the key to addressing the health and social needs of older people and reducing the risk factors driving the increased and costly need for long-term care. At the same time, the effects of downsizing and cost constraints in all segments of today's society challenge our ability to address these needs. Although scientists today face serious challenges to completing the work that research already has generated and to initiating new projects, we are energized by the potential for widespread benefit. Using that energy, in 20 years' time we should expect to look back with the same sense of accomplishment and ahead with the same enthusiasm for achievements yet to come.

Genetic relationships of Mlsa among polymorphic loci on distal mouse chromosome 1

The segregation of Mlsa with respect to genes localized distally on mouse chromosome 1 was examined in two sets of recombinant inbred (RI) strains. In order to localize Mlsa, a linkage map based on analysis of both interspecific backcross mice and multiple sets of RI strains was utilized: (centromere) - Ren-1,2 - 10 centimorgans (cM) - At-3 - 8cM-Apo-A2/Ly-17 - 2cM - Spna-1 - 4cM - Akp-1 - (telomere). The Mlsa allele was mapped to a region that extended just centromeric of Ly-17 (one crossover in 40 RI strains) to just telomeric of Spna-1 (no crossover in 40 RI strains). The identification of multiple polymorphic loci in the region of Mlsa should allow precise gene localization and assist in efforts to clone this gene.

Mouse endogenous superantigens: Ms and Mls-like determinants encoded by mouse retroviruses

Commonly used inbred mouse strains express different combinations of integrated mouse mammary tumor proviruses (MMTV). This appendix summarizes the proviruses that have been detected. The reported functional properties of those MMTV proviral products which have been identified as superantigens are also summarized, including the ability to elicit primary or secondary T cell responses and to induce Vb-specific clonal deletion during T cell differentiation. In addition, the amino acid sequences of putative ORF gene products of different MMTV are compared.

The expression and functional involvement of nuclease- specific idiotype on nuclease-primed helper T cells

The expression and functional significance of idiotypic determinants on antigen-specific helper T (Th) cell populations for responses to Staphylococcal nuclease (Nase) were evaluated in an in vitro antibody response system. Trinitrophenyl (TNP)- specific plaque-forming cell responses to TNP-conjugates of Nase (TNP-Nase) were shown to require the cooperation of Nase-primed Th cells as well as unprimed B and accessory cells. The expression on these antigen-primed Th cells of idiotypic determinants cross-reactive with those on anti-Nase antibodies was demonstrated by the specific elimination of Th cells for TNP-Nase by treatment with affinity-purified anti-idiotypic antibodies plus complement. The susceptibility of Nase-primed Th cells to elimination by such treatment was specific in that anti-idiotypic antibodies affected Th cells only from strains normally expressing the same (or a cross-reactive) idiotype on anti-Nase antibodies. A functional role of the idiotypes expressed on Nase-primed Th cells was suggested by the fact that anti-idiotypic antibody present throughout the period of culture, in the absence of complement, suppressed responses to TNP-Nase in an antigen- and strain-specific manner. It was further shown, by cell mixing experiments, that this inhibition appeared to occur at the level of the Th cells and was not dependent on the strain of origin of the B cells. Thus, antigen-specific Nase-primed Th cells express strain-specific idiotypic determinants cross-reactive with, or identical to, those of anti-Nase antibodies. These cell surface idiotypic determinants appear to be functionally involved in the activity of Th cells for the induction of antibody responses to TNP-Nase in vitro.

Mixed lymphocyte reactivity and cell-mediated lympholysis to D-end differences of the murine major histocompatibility complex. Comparison of in vitro responses to exclusive D-end or more extensive MHC differences

In vitro mixed lymphocyte culture (MLC) responses and the in vitro induction of cell-mediated lympholysis (CML) were studied in congenic strain combinations in which the responding and stimulating strains differed either at the entire major histocompatibility complex (MHC) or only at the D end of the MHC. In contrast to previously reported studies, the relative strengths of stimulation by 'D end only' differences or by whole MHC differences were examined by stimulating identical responding populations with titrated numbers of stimulating cells that differed from the responder either at the D end only or over the entire MHC. When tested in this manner isolated D-end differences were sufficient to generate significant MLC and CML responses in each combination tested. Several 'D end only' differences (the responses of B10.A to B10.A(2R); of B10.A(2R) to B10.A; of B10.D2 to B10.HTG; and of B10.HTG to B10.D2 were several fold less efficient in stimulating MLC and CML responses than were control stimulating cells differing over the whole MHC. In contrast, when the mutant D-end allele da was present on the stimulating cell (the responses of B10.D2 to B10.D2(M504) and of B10 to B10.D2(R106)), stimulation by an isolated D-end difference was comparable to stimulation by broader MHC differences. These findings are discussed in terms of the possible functional complexity of the D region.

Immunoglobulin (Ig) mu, kappa transgenic mice express transgenic idiotype on endogenously rearranged IgM and IgA molecules by secretion of chimeric molecules

The sera of C57BL/6 mice transgenic for a mu a allotype heavy (H) chain and kappa light chain gene contained endogenous nontransgene immunoglobulin (IgM) (mu b allotype) and IgA molecules which carried the idiotype expressed by the transgenically encoded IgM (mu a) molecule. Serological analysis demonstrated that the presence of the transgenic idiotype on endogenous IgM and IgA was caused by the secretion of chimeric molecules that carried both chains encoded by the mu a transgene and products of endogenously rearranged Ig mu b or alpha genes. These and other results suggest that allelic exclusion of Ig gene rearrangement in mu, kappa transgenic mice is not absolute, that B cells can secrete Igs composed of more than a single (H) chain type, and that endogenous isotype switching does not result in a complete silencing of transgene expression.

Regulatory mechanisms in cell-mediated immune response. V. Distinct Lyt subsets mediate antigen-specific and antigen-nonspecific suppression

These studies were undertaken to assess the T cell subpopulations mediating antigen-specific as well as antigen-nonspecific suppression of cytotoxic T lymphocyte (CTL) responses to alloantigens. It was first demonstrated that generation of the CTL response itself requires Lyt 1+2+ T cells. Subsequent studies then characterized two distinct suppressor pathways that regulate the CTL response. Antigen nonspecific suppression was mediated by Lyt 1+2-Ts cells that were generated during in vitro culture from an Lyt 1+2- precursor population. In a second pathway, antigen-specific suppression was mediated predominantly by Lyt 1-2+ Ts cells that were activated during the in vitro allosensitization of Lyt 1+2+ precursors. Thus, the in vitro CTL response to alloantigens is modulated by two different pathways of T-cell-mediated suppression, and these pathways are mediated by distinct Lyt-defined T cell subpopulations.

Helper T cell requirements for T15 idiotype expression on phosphorylcholine-specific antibodies

The requirement for idiotype-specific T cells was investigated in the T15 idiotype-dominant T cell-dependent response of unprimed BALB/c and (BALB/c X C57BL/6)F1 B cells to phosphorylcholine (PC). It was first demonstrated that cloned keyhole limpet hemocyanin (KLH)-specific, major histocompatibility complex (MHC)-restricted T helper (Th) cells as well as heterogeneous KLH-primed Th populations were capable of generating PC-specific antibody responses in T-depleted unprimed B cell populations cultured in the presence of PC-KLH. The PC-binding antibody responses generated under these conditions were indistinguishable when assayed for carrier-hapten linkage requirements, immunoglobulin isotype (predominantly IgM) or PC affinity. Further, it was observed that the PC-binding antibodies which were generated in the presence of these two T cell populations expressed equivalently high levels of T15 idiotype. Assaying antibody and idiotype by either enzyme-linked immunosorbent assay or plaque-forming cell assay yielded similar results. Since monoclonal MHC-restricted, KLH-specific Th cells presumably lack any additional T cell populations, these results argue against an absolute requirement for anti-idiotypic Th cells in the generation of T15-dominant antibody responses.

Different specificities of cloned T cells assessed by in vitro proliferation assays and by the ability to mediate skin graft rejection in vivo

The experiments presented here have compared the specificities of T cell clones as determined by in vitro proliferative responses and their specificities as reflected by their ability to mediate skin graft rejection in vivo. Two proliferative T cell clones with distinct in vitro specificities were evaluated for their ability to mediate rejection of skin grafts from C57BL/10 Scn nu/nu mice. Clone 14.11 (L3T4+, Lyt2-) was specifically stimulated to proliferate in vitro by I-Ad determinants, while clone 3.3.10 (also L3T4+, Lyt2-) recognized M1sa products in the context of MHC-encoded cell surface determinants. The results demonstrate that both clone 14.11 and clone 3.3.10 T cells are capable of mediating rejection of DBA/2 (H-2d, M1sa) skin grafts from B10 nu/nu mice. Surprisingly, neither clone 3.3.10 T cells nor clone 14.11 T cells were found to be effective at rejecting skin grafts from the D1.C congenic donor strain of mice (also H-2d, M1sa) from B10 nu/nu mice. Further, clone 14.11 T cells were also found to be ineffective at rejecting B10.D2 (H-2d, M1sb) skin grafts from B10 nu/nu mice. These data indicate the existence of a striking dichotomy between the specificity of alloreactive T cell clones as determined by in vitro proliferation studies and their functional capabilities in vivo.

Tissue-specific and growth-regulated expression of CD44 variable exon determinants in the mouse

CD44 is a polymorphic transmembrane glycoprotein widely expressed in lymphocytes and epithelial cells. CD44 polymorphism reflects both posttranslational modification and alternative splicing of up to 10 variably expressed exons in the membrane-proximal CD44 extracellular domain. An analysis of CD44 variable exon-containing isoforms in the mouse was carried out by generating a panel of monoclonal antibodies against variable region determinants of CD44. Immunohistochemical analysis demonstrated selective patterns of expression of CD44 variable exon determinants in normal tissues, and flow cytometric analysis identified expression of CD44 variable exon-dependent determinants in epithelial and lymphoid cell lines. Regulation of alternative splicing was studied by characterization of cell surface expression of CD44 variable exon determinants on HC11 mammary epithelial cells, and it was demonstrated that variably spliced isoforms are selectively regulated as a function of growth phase in vitro. These results demonstrate the tissue-specific and growth-regulated expression of the CD44 isoform at the level of cell surface protein products and identify isoform-specific determinants that can be targeted in analysis of isoform-specific function.

T cell regulation of B cell activation. Lyt-1+,2-T cells modify the MHC-restricted function of heterogeneous and cloned T suppressor cells

Previous studies have shown the existence of both heterogeneous Lyt-1-,2+ suppressor (Ts) cells and cloned Lyt-1+,2- Ts cells which, despite the difference in their Lyt phenotypes, functioned in a similar antigen-specific and major histocompatibility complex (MHC)-restricted fashion to suppress the antibody responses generated by cloned helper T (Th) cells and hapten-primed B cells. Our studies were carried out to assess in further detail the genetically restricted cell interactions that mediate this immune response suppression. We show that the activation of both heterogeneous and cloned Ts cells is antigen-specific and MHC-restricted under our experimental conditions. After appropriate activation, the effector function of both cloned Lyt-1+,2-Ts cells and heterogeneous Lyt-1-,2+ Ts cells was also antigen-specific. In contrast, once activated, Ts cells suppressed the responses generated by cloned Th cells and hapten-primed B cells in an MHC-unrestricted fashion. We also showed, however, that a population of unprimed Lyt-1+,2-T cells was able to significantly alter the genetic restriction requirements for Ts cell function. The activity of this population was itself MHC-restricted, and was observed only when the unprimed Lyt-1+,2-T cells shared the MHC restriction specificity of the cloned Th cells functioning in a given response. When these requirements were satisfied, Lyt-1+,2- T cells significantly modified the suppression mediated by both heterogeneous and cloned Ts cells, resulting in suppression that was then MHC restricted in its effector function as well as in its activation requirements. Thus, our findings suggest that the observed MHC restriction in Ts function is the result of a complex interaction involving Ts cells, Th cells, and an additional population of MHC-restricted Lyt-1+,2- T cells. This newly characterized activity of Lyt-1+,2- T cells functionally resembles that of an MHC-restricted contrasuppressor population that selectively blocks a pathway of MHC-unrestricted Ts activity, while leaving intact susceptibility to MHC-restricted Ts effects.

Immune responses against self-TCR peptides

Vaccination of rats against the TCR peptide V beta 8.2 (39-59) was reported to inhibit the immunopathogenic process of EAE. Analysis of the immune response to this peptide and several related TCR peptides yielded the following findings: (i) Lewis rats immunized in vivo and challenged in vitro responded with vigorous lymphocyte proliferative responses to peptide V beta 8.2 (39-59) and to three other rat TCR peptides, V beta 8.3 (15-32), V beta 8.3 (39-59), and V beta 14 (39-59). On the other hand, two other rat peptides, V beta 8.2 (18-38) and V beta 8.3 (62-76), were poorly immunogenic. (ii) Rat peptide V beta 8.2 (39-59) was found more immunogenic than its mouse homolog, in both Lewis rats and B10.A mice. A moderate level of cross-reactivity was observed between these two peptide homologs. (iii) Rats of different genetic makeups varied in their response to peptide V beta 8.2 (39-59). A similar pattern of response of the different rats was found with another TCR peptide, V beta 14 (39-59). Hybrids between high and low responder rat strains resembled the high responders in their response to the TCR peptides. (iv) Sensitized lymph node cells as well as lymphocytes of a cell line specific for peptide V beta 8.2 (39-59) failed to respond to T cells that express the V beta 8.2 gene product. This observation is interpreted to indicate that peptide V beta 8.2 (39-59) is a cryptic determinant of the V beta 8.2 protein. Moreover, the data suggest that lymphocytes proliferating against peptide V beta 8.2 (39-59) may not be responsible for the reported inhibition of EAE in rats vaccinated with this peptide.

Mls determinants recognized by T cells

The relationship among different minor lymphocyte stimulatory locus (Mls) determinants, Mlsa, Mlsb, Mlsc and Mlsd, remains unclear. Because of the high degree of cross-reactivity between Mlsa and Mlsd determinants, the weak stimulatory capacity of Mlsc, and the generally non-stimulatory nature of Mlsb, some investigators have recently suggested that Mls is composed of only a single expressed allele originally defined as the a and d alleles. In order to clarify the nature of Mls determinants, T cell clones positively selected for reactivity to the three stimulatory Mls determinants, Mlsa, Mlsc and Mlsd, were generated and their specificities defined by extensive genetic studies. The response pattern of these Mls-specific clones as well as the results of primary mixed lymphocyte responses indicated that: (i) Mlsa and Mlsc determinants recognized by T cells are distinct, demonstrating that polymorphism does exist within the Mls system; and (ii) Mlsd is not an independent Mls type since Mlsd determinants are composed of Mlsa and Mlsc determinants and anti-Mlsd T cell responses are, in fact, the sum of anti-Mlsa and anti-Mlsc responses.