Two different VH gene products make up the T-cell receptors

Antigen receptors on murine T lymphocytes in contact sensitivity. I. Functional inhibition of effector T cells by monovalent 2,4-dinitrophenol: implication for a two-receptor model

Experiments were done to investigate the nature of the antigen receptor on lymph node(LN) T cells from mice sensitized to 2,4-dinitrofluorobenzene (DNFB). LN cells or purified T cells were treated in vitro with monovalent or different multivalent 2,4-dinitrophenol (DNP) ligands. The effect of this treatment was measured by testing the ability of the cells to transfer contact sensitivity (CS) to DNFB into naive recipients. We found that treatment of the T cells in vitro with either epsilon-DNP-L-lysine or DNP-protein conjugates inhibits the transfer of CS in a dose-dependent way. The inhibition is hapten specific and is not mediated by activation of suppressor cells. Inhibition of the T cells by hapten in vitro is rapid (15-30 min) and temperature independent but requires divalent cations in the treatment medium. In addition, it was found that hapten-treated T cells are unable to adsorb specific anti-idiotype antibody, and this inhibition of adsorption is hapten specific. Collectively, these data indicate that DNFB-immune T cells express a receptor specific for the hapten DNP and provide evidence that supports a two-receptor model for T cell recognition of antigen.

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.

Murine syngeneic mixed lymphocyte response. I. Target antigens are self Ia molecules

A system has been described that produces a murine syngeneic mixed lymphocyte response (MLR) comparable in magnitude to an allogeneic MLR. The responder cells in these cultures exhibit the classic immunologic characteristics of both memory and specificity. Studies using radiation-induced bone marrow chimeras of F(1) {arrow} parent type indicated that, similar to many other T cell-mediated immune responses, the response of the T lymphocytes in the syngeneic MLR was major histocompatibility complex-restricted and was determined by the environment in which the T cells matured. Using responder T cells from F(1) {arrow} parent chimeras and stimulator cells from H-2 recombinant strains, it was possible to map the genes involved in the stimulation to the K and/or I regions. In addition, blocking studies with monoclonal anti-Ia antibodies suggested that in the B10.A strain the critical molecules were products of both the I-A(k) and I-E(k) subregions. The issue of whether the syngeneic MLR is directed solely at self I-region antigens or whether the response represents proliferation to an unknown antigen in association with self I-region determinants was also addressed. Secondary syngeneic MLR were successfully performed in normal mouse serum and with stimulator cells prepared in the absence of bovine serum albumin to rule out the possibility that xenogeneic serum antigens were involved in the stimulation. The possibility that the syngeneic MLR might represent a secondary response to environmental antigens was eliminated by using germ- free mice as a source of stimulator cells and by demonstrating that spleen cells from unimmunized, fully allogeneic chimeras (B10.A {arrow} B10) could generate a normal syngeneic MLR even though such chimeras could not be primed to respond to any foreign antigens unless supplemented in vivo with a source of antigen-presenting cells syngeneic to the B10 host. The possibility that the syngeneic MLR was a primary response to a foreign antigen was considered unlikely because by using our culture conditions we could not obtain a primary antigen response or a secondary antigen response after in vitro priming to a variety of potent foreign antigens. Finally, the possibility that the syngeneic MLR represents a response to a variety of minor histocompatibility self antigens in association with self Ia molecules was eliminated by showing that the secondary responses to H-2 compatible, non-H-2 different strain (A/J vs. B10.A and C3H, or BALB/c vs. B10.D2 and DBA/2) were comparable to the secondary responses to syngeneic stimulators. Thus, we conclude that the target antigens in the syngeneic MLR are solely determinants on self Ia molecules, although the functionally equivalent possibility of a single, nonpolymorphic, minor self antigen seen in association with self Ia molecules cannot be excluded.

A one-receptor view of T-cell behaviour

The discovery of T cells and their behaviour has forced a re-evaluation of the immunological relationship between self and not-self. T cells seem to respond against foreign antigens only when the latter are in some form of association with self molecules encoded by the major histocompatibility complex. This has raised the question of whether T-cell recognition may depend on two separate receptors. I present here the case for a model of T-cell behaviour based on a single receptor.

Anti-receptor antibody-induced suppression of murine H-Y-specific delayed-type hypersensitivity responses

A putative anti-H-Y receptor antiserum (ARA) was raised in C57BL/6 male mice against splenic T lymphocytes from syngeneic females immunized against H-Y antigen. When this antiserum is given i.v. to C57BL/6 females it prevents the expression of H-Y-specific delayed-type hypersensitivity (DTH). The suppressive activity in ARA was selectively retained on rabbit anti-mouse immunoglobulin columns, and could be absorbed by H-Y-immune spleen cells from C57BL/6 female mice. The abrogation of H-Y DTH reactivity was at least in part due to the generation of suppressor T cells which are generated by ARA in naive female mice. ARA-generated suppressor cells specifically inhibit the induction phase of DTH responses to the H-Y antigen, having no effect on (4-hydroxy-3-nitrophenyl)acetyl (NP)-specific cutaneous sensitivity responses or on DTH responses to minor histocompatibility antigens. Furthermore, there is a requirement for Igh gene homology between the strain producing the ARA and the strain in which the DTH response is induced. Thus, C57BL/6 ARA given to A.BY (H-2b, Igh-1e) or to B.C-8 (H-2b, Igh-1a) mice was unable to suppress homologous H-Y DTH responses in these strains. However, C57BL/6 ARA induced suppressor cells in B.C-8 mice which were capable of inhibiting H-Y DTH responses when adoptively transferred to C57BL/6 females.

Antigen-inducible, H-2-restricted, interleukin-2-producing T cell hybridomas. Lack of independent antigen and H-2 recognition

We developed a method for production of antigen-specific, H-2-restricted T cell hybrids. The tumor cell partner in the fusions was itself a T cell hybrid, FS6-14.13.AG2 (or its derivatives), which could be induced to produce the growth factor, interleukin-2 (IL-2), in response to a challenge with concanavalin A, but had no known antigen specificity. The normal T cell partner in the fusions was a population of lymph node T cell blasts that had been highly enriched in antigen-specific, H-2-restricted T cells by in vivo immunization, followed by in vitro challenge with antigen and clonal expansion in IL-2-containing medium. These fusions produced hybrids that grew constitutively in culture. A sizable proportion of the hybrids demonstrated the ability to produce IL-2 in response to a challenge with specific antigen presented by irradiated spleen cells of the appropriate H-2 type. Four cloned antigen/H-2-specific hybrid lines were produced. AO-40.10 responded to chicken ovalbumin (OVA) when presented by I-A(k)-bearing cells. DC1.18.3 responded to the apo form of beef cytochrome c when presented with I-A(d). AODK-10.4 responded to keyhole limpet hemocyanin (KLH) presented with I-A (d). AODK-1.16 also responded to KLH presented by a product of the I region of H-2(d), but the data were consistent with either a product of the I-J-I-E(d) region or a combinatorial molecule with elements from both I-A(d) and I-E(d)/I-C(d). Coincidentally, AO-40.10 was shown to have an unexpected alloreactivity with a product of H-2(b) mapping to the K-I-A region. These hybrids should prove invaluable as sources of monoclonal material for the study of the receptor(s) on T cells with H-2-restricted antigen specificities. We also generated T cell hybrids with two antigen/H-2 specificities by fusing an azaguanine-resistant clone of AO-40.10 to normal T cells with a different antigen/H-2 specificity. Many of the hybrids retained reactivity to OVA plus H-2(a) and to the second antigen/H-2 combination. None reacted to either OVA plus the second H-2 type or to the second antigen plus H-2(a). One of these hybrids was successfully cloned to produce the line AOFK- 11.11.1. It retained the ability to recognize OVA plus I-A(k) inherited from one parent, and KLH plus IA(f) inherited from the other. It did not recognize OVA plus IA(f) or KLH plus I-A(k). These results have some bearing on models describing the nature of T cell receptors for antigen recognized in association with H-2 products. They do not support models in which antigen and H-2 are recognized separately by two independent T cell receptors.

Specificity of antigen binding by T cells; competition between soluble and Ia-associated antigen

Competitive antigen binding experiments were performed with purified T and B cells of C3H.SW (H-2b) mice. As antigen, (T,G)-A--L [poly-L(Tyr,Glu)-poly-DL-ALa-poly-L Lys] was used, both in an Ia-containing form, released by adherent cells (IAC-Puri and Lonai, Eur. J. Immunol. 1980. 10:273), and in regular solution. It was found that regular (T,G)-A-L did not compete with the binding of 125I-labeled-IAC-(T,G)-A--L even at a 10(4)-fold excess, whereas IAC-(T,G)-A--L inhibited binding at 10-fold excess. The specificity of (T,G)-A--L binding to high-responder T and B cells was compared by using related branched synthetic copolymers as competitors. B cells cross-reacted with (T,G)-A--L, (H,G)-A--L, (G)-A--L and (T,G)-Pro--L. In contrast, antigen binding C3H.SW T cells cross-reacted only with (T,G)-A--L and (Phe, G)-A--L to both of which they are Ir gene-controlled high responders. Evidence for the Ir gene control of IAC-binding T cells was obtained by showing that high X low responder F1 hybrid T cells preferentally bind IAC-(T,G)-A--L processed by processor cells deriving from the high-responder parental strain. These data are interpreted to suggest that T cells have high affinity for antigen plus self Ia complexes, whereas they have a much lower, if any, affinity for free antigen. It also follows from the results that the structure of the complex ligand may have a role in defining the specificity, H-2 restriction and Ir gene control of T cells.

Selected populations of alloreactive T cells contain helper T cells but lack ThId, an antigen-specific helper T cell required for dominant production of the T15 idiotype

Isolated, alloreactive T cell populations were primed with protein carriers in vivo and tested for their ability to provide help for an anti-phosphorylcholine (PC) antibody response and for production of the T15 idiotype. It was found that alloreactive T cell populations would support anti-PC antibody response but did not selectively activate B cells capable of producing the T15 idiotype that normally dominates such responses. This failure to help for the production of the T15 idiotype was shown to be due to the absence of an antigen-specific helper T cell that is required for dominant idiotype production (ThId). These studies suggest that ThId cells have recognition structures for antigen and for self idiotype, but lack recognition structures for major histocompatibility complex-encoded antigens.

Antigen-specific T cell clones restricted to unique F1 major histocompatibility complex determinants. Inhibition of proliferation with monoclonal anti-Ia antibody

The existence of T cells specific for soluble antigens in association with unique F(1) or recombinant major histocompatibility complex (MHC) gene products was first postulated from studies on the proliferative response of whole T cell populations to the antigen poly(Glu(55)Lys(36)Phe(9))(n) (GLphi). In this paper we use the newly developed technology of T lymphocyte cloning to establish unequivocally the existence of such cells specific for GLphi and to generalize their existence by showing that F(1)- specific cells can be isolated from T cell populations primed to poly(Glu(60)Ala(30)Tyr(10))(n) (GAT) where such clones represent only a minor subpopulation of cells. Gl.4b-primed B10.A(5R) and GAT-primed (B10.A x B10)F(1) lymph node T cells were cloned in soft agar, and the colonies that developed were picked and expanded in liquid culture. The GLphi-specific T cells were then recloned under conditions of high-plating efficiency to ensure that the final colonies originated from single cells. T cells from such rigorously cloned populations responded to stimulation with GILphi but only in the presence of nonimmune, irradiated spleen cells bearing (B10.A x B10)F(1) or the syngeneic B 10.A(5R) recombinant MHC haplotype. Spleen cells from either the B10 or B 10.A parental strains failed to support a proliferative response, even when added together. (B10 x B10.D2)F(1) and (B10 x B10.RIII)F(1) spleen cells also supported a proliferative response but (B10 x B10.Q)F(1) and (B10 X B10.S)F(1) spleen cells did not. These results suggested that the T cell clones were specific for GL[phi} in association with the beta(AE)(b)-alpha(E) (k,d,r,) Ia molecule and that recognition required both gene products to be expressed in the same antigen-presenting cells. Support for this interpretation was obtained from inhibition experiments using the monoclonal antibody Y-17 specific for a determinant on the beta(AE)(b)-alphaE Ia molecule. Y-17 completely inhibited the proliferative response of a GLphi-specific clone but had no effect on the response of either a PPD-specific or GAT-specific clone, both of which required the beta(A)-alpha(A) Ia molecule as their restriction element. No evidence could be found for the involvement of suppressor T cells in this inhibition. We therefore conclude that the phenomenon of F(1)-restricted recognition by proliferating T cells results from the presence of antigen- specific clones that must recognize unique F(1) or recombinant Ia molecules on the surface of antigen-presenting cells in addition to antigen in order to be stimulated.

T cells respond preferentially to antigens that are similar to self H-2

We have constructed bone marrow irradiation chimeras to investigate the influence of self antigens on the specificity of the T lymphocyte receptor repertoire. Bone marrow cells from (A X B)F1 mice heterozygous for the major histocompatibility genes were allowed to mature into T cells in irradiated parent A or parent B strains. More than 8 weeks after irradiation, when the lymphoid system had regenerated from the F1 stem cells, the degree of T cell reactivity to mutant major histocompatibility antigens, A', was assessed. It was found that T cells that had matured in the irradiated A mice, [F1 leads to A] chimeras, responded better to A' antigen than did T cells from the [F1 leads to B] chimeras. Because the mutant histocompatibility antigen A' is very similar in structure to A, differing only by one or a few residues, this suggests that the T cell repertoire in [F1 leads to parent] chimeras reacts preferentially with foreign antigens that are slight variants of the self antigens expressed on radiation-resistant cells--probably cells in the thymus.

Comparison between the specificity of primary and secondary killer cells against alloantigens and hapten-modified syngeneic lymphoid cells

Cytotoxic responses of lymphoid cells from different mouse strains against syngeneic cells modified with the haptens fluorescein isothiocyanate and trinitrophenyl were investigated. Mic of the H-2k strain demonstrated strong primary in vitro hapten-specific cytotoxicity reactions, which were H-2 restricted and involved the Kk specificity. However, cells from H-2d and H-2b mice developed hapten-specific cytotoxic reactions that showed H-2 cross-reactivity. This cross-reactivity, with regard to the restriction element, was particularly evident with cells from mice that had been immunized in vivo. No cross-reaction was observed between the two haptens, and Dd target cell antigens. Similar cross-reactions were demonstrated in vitro experiments in which secondary in vitro responses were induced by stimulation with cross-reacting H-2 antigens. This finding was also investigated in allogeneic cytotoxicity. In vitro induced responses resulting in relatively weak specific cell-mediated lympholysis reactions were H-2 specific, whereas secondary in vitro responses demonstrated cross-reactivity between Dd and Db antigens. In these test systems, cross-stimulation was also demonstrated in secondary in vitro responses. These results are discussed in terms of similarities of T cell recognition of hapten-modified self antigens and of alloantigens.

Antigen-reactive T cells can be activated buy autologous macrophages in the absence of added antigen

T cells responsive to macrophages (M phi) in the autologous mixed lymphocyte reaction (AMLR) contain those cells that can be induced to proliferate by soluble antigens. Negative solution (5-bromo-2-deoxyuridine and light) of T cells activated by autologous M phi also removed those cells required for reactivity to Candida albicans and purified protein derivative. Positive selection of T cells responsive to autologous M phi yields a population that is simultaneously enriched in antigen reactivity. Some patients demonstrating cutaneous anergy and diminished in vitro blast transformation in response to soluble antigen also lack T cells responsive to the AMLR to M phi. When considered in conjunction with previously reported data, these findings indicate the AMLR occurring between T cells and M phi in the absence of soluble antigen represents self recognition occurring between antigen-reactive T cells and antigen-presenting M phi.

Allogeneic H-2 dose not cross-react, at the helper T-cell level, with Hapten-modified Self

Helper T cells raised in CBA mice and enriched in vitro with specificity for trinitrophenylmodified syngeneic spleen cells can activate hapten-modified B cells bearing Ik. These helper cells fail to activate B cells expressing any of six independent I-region haplotypes, indicating lack of cross-reactivity between hapten-self and allogeneic I-region products. Furthermore, hapten-derivatized allogeneic B cells are also not activated, demonstrating that the elements restricting T-cell function are poorly, if at all, cross-reactive.

Antigen-binding receptors on T cells from long-term MLR. evidence of binding sites for allogeneic and self-MHC products

Antibody inhibition of radiolabelled stimulator membrane vesicle binding by T blasts activated in the mixed lymphocyte reaction (MLR) was used to identify responder-cell determinants involved in the binding phenomenon. Antisera or monoclonal antibodies against Thy-1, Lyt-1, Lyt-2 and Ly-6 antigens were not inhibitory. However, antibodies against heavy-chain V region (VH) determinants strongly inhibited vesicle binding by both primary and long-term MLR blasts. Anti-Ia (both alloantisera and monoclonal reagents) caused inhibition of antigen binding by primary MLR blasts only. T blasts from long-term MLR lines were neither Ia-positive, nor susceptible to blocking of antigen binding with anti-Ia. However, these cells were capable of specifically absorbing soluble syngeneic Ia material, with the concomitant appearance of vesicle-binding inhibition with anti-Ia sera. Acquisition of syngeneic Ia by T blasts was effectivelly blocked with the anti-VH reagent. Passively bound self-Ia did not interfere with vesicle binding in the absence of anti-Ia. These results strongly suggest the existance of specific self-Ia acceptor sites closely linked to the receptors for stimulator alloantigens on T cells proliferating in MLR. A receptor model based on these findings is briefly discussed.

Anti-self receptors. I. Direct detection of H-2L region-restricted receptors on murine thymocytes

A high proportion (20--50%) of murine thymocytes form rosettes with either syngeneic or allogeneic erythrocytes. The specificity of this interaction was investigated by measuring the ability of different erythrocyte sonicates to inhibit rosette formation. With erythrocyte sonicates from recombinant mouse strains it was demonstrated that rosetting with syngeneic erythrocytes was mediated by H-2L and/or H-2D region-restricted receptors. The specificity of autorosetting was directly mapped to the H-2L region by the inability of erythrocyte sonicates from the BALB/c-H-2dm2 mutant, an H-2L-deletion mutant, to inhibit the rosetting of wild-type (BALB/c) thymocytes. The B10,2D2-H-2dm1 mutant, which has substantially modified H-2L and H-2D antigens, supported this conclusion. Furthermore, anti-H-2L sera were able to specifically block the inhibition of rosetting by erythrocyte sonicates. The above procedures clearly implicated the H-2L region in the thymocyte rosetting of d and k haplotypes. With the s haplotype the rosetting receptor was mapped to the H-2L/H-2D region, whereas with the b and q haplotypes rosetting was only mapped to the D end of the H-2 complex. This study also suggested complete cross-reaction between the thymocyte receptors carried by the k and d haplotypes, whereas the receptors of b, q, and s haplotypes were haplotype specific. In addition, the inhibition assay indicated that the rosetting of thymocytes with allogeneic and xenogeneic (rat) erythrocytes was mediated by a receptor primarily directed against self-H-2L. Finally, the critical role played by the H-2L region in this rosetting phenomenon was demonstrated by the inability of thymocytes from the H-2L-deletion mutant (H-2dm2) to rosette with syngeneic, allogeneic (rat) erythrocytes.

Three-receptor, clonal expansion model for selection of self-recognition in the thymus

The postulate is made that dual recognition by T lymphocytes is due to two types of receptor, one encoded by antibody genes and one by a distinct multigene family with simple rules for expression. This postulate leads to a model explaining ontogenic and evolutionary selection for self recognition, T lymphocyte effector function, the apparent high frequency of alloreactive T cells and immune response gene activity. The model is contrasted with previous explanations of self-recognition phenomena.

Suppression of T cells specific for the nonthymic parental H-2 haplotype in thymus-grafted chimeras

The mechanism of restriction of T-cell specificity by the genotype of the thymus in allogeneic and semiallogeneic chimeras was investigated. Lack of induction of delayed-type hypersensitivity (DTH) directed against antigen in association with the nonthymic parental haplotype in naive cells adoptively transferred into chimeras suggests the existence of an in vivo suppressive mechanism. However, it was not possible to suppress the expression of DTH in sensitized cells transferred into chimeras, or to transfer this suppression to normal naive recipients.

Idiotypes, T-cell receptors, and T-B cooperation

T cells are responsible for virtually all the characteristics of the mammalian immune system except the production of serum antibody, in which they play a vital regulatory role. As such, they are central to our understanding of the immune system. T cells recognize cell-bound antigens with great precision, in association with self MHC antigens. They do this by means of antigen-specific receptors, whose antigen-combining sites are encoded in conventional VH genes. There is evidence that T cells carry at least two kinds of specific receptors, one for MHC antigens and one for non-MHC antigens. Both of these would bear VH-encoded and distinct idiotypic determinants. The process by which antigens associate with MHC-gene products on cell surfaces is poorly understood at present, and so is the process by which the two types of receptors communicate with each other. T cells are divisible into a number of subpopulations playing unique functional roles in the regulation of antibody responses. If one examines them further for other functions, even greater complexity emerges. Thus, all T cells may not have the same kind of receptor, which would not be surprising given the wide variety of functions they perform. Future work will undoubtedly focus on these important questions.

T cells that encounter virus in the complete absence of a particular H-2 antigen are nonresponsive when stimulated again in the context of that H-2 antigen

Immunologically naive BALB/c (H-2d) and C57BL/6J (B6) (H-2b) T-cell populations can, after filtration to remove alloreactive precursor lymphocytes, be induced to respond to vaccinia virus presented in the context of H-2Kk when stimulated in an appropriate recipient. Exposure to vaccinia virus 6 wk previously completely abrogated the capacity of BALB/c T cells to interact with H-2Kk-vaccinia virus. This is also true for negatively selected B6 thoracic duct lymphocytes taken at 14 or 18 d, but not at 6 wk after immunization: the discrepancy is thought to reflect the progressive emergence of new T cells in the latter group. No evidence could be found for the operation of suppression, and the results are considered to indicate that T cells that interact with virus in the absence of the relevant H-2 antigen are tolerized. Whereas stimulation to effector function is H-2 restricted, induction of immune paralysis may be unrestricted. The capacity of T-cell populations to respond to virus presented in the context of allogeneic H-2 determinants thus depends upon previous antigenic experience.

Surface Ig on rabbit lymphocytes. Rabbit B and T cells are distinct populations

Rabbit peripheral blood lymphocytes (PBL) were analyzed by immunofluorescence using anti-T cell conjugates and anti-Fab, anti-a1 allotype, anti-IgM and anti-IgA conjugates. In addition, T cells were demonstrated by rosetting with papain-treated homologous erythrocytes. Control experiments, using acid treatment and incubation at 37 degrees C for 18 h after or without pronase treatment, revealed the endogenous origin of all surface determinants tested. A good correlation was found between results obtained with the two anti-T cell conjugates used and the T rosette test on PBL and on lymphoid cells isolated from various organs. In lymphocytes isolated from peripheral blood and from various lymphoid organs, the percentages of T and B cells were respectively 45 and 38 for PBL, 10 and 46 for bone marrow, 27 and 31 for appendix, 40 and 45 for spleen, 42 and 46 for Peyer's patches, 96 and 0.3 for thymus and 70 and 16 for peripheral lymph nodes. The percentage of "null" cells in lymphocyte populations derived from bone marrow and appendix is rather high. The final percentages of T and B cells in rabbit PBL depend to a significant extent on the method of isolation, especially isolation by Ficoll-Hypaque centrifugation results in a depletion of T cells. Moreover, a rather impure lymphoid cell suspension is obtained. In double incubation experiments, T cells (as defined by T cell antigen(s) or rosette formation) and B cells (Fab-bearing cells) were entirely different subpopulations. Allotypes of the a locus could not be detected on the surface of T cells. The results are discussed with respect to genetic coding of antigen receptors on B and T cells.

Rat memory T lymphocytes. II. Differences in macrophage-dependent activation shown by Actinomyces viscosus antigens and by mitogens, using silica in vitro

Protein-coated silica, a macrophage toxin, was used to assess the requirement for accessory cells in the induction of an in vitro proliferative response to (i) antigens from Actinomyces viscosus and (ii) the mitogens conconavalin A (Con A) and phytohaemagglutinin (PHA). T cells were obtained from RIC-Sprague-Dawley rats primed in vivo with A. viscosus Nyl by splenectomy and filtering the spleen cell suspensions through Degalan Ig-anti-IgG columns. In the presence of 100 microgram silica/ml during 4 days of culture, the proliferative response of T lymphocytes was not diminished. In contrast, when the T cells were precultured with silica for 24 h, washed, and subsequently cultured with the antigen fractions, antigen-induced proliferation was abolished. This procedure, however, had no influence on mitogen-induced proliferation was abolished. This procedure, however, had no influence on mitogen-induced T-cell activation. It is therefore concluded that the antigen-dependent anamnestic in vitro response (but not activation by mitogens) of rat T lymphocytes needs help from silica-sensitive macrophages.

Alloantigens derived from stimulator cells and bound onto MLC-activated rat T lymphoblasts

Rat T lymphocytes were activated in MLC (mixed leucocyte culture) against allogeneic stimulator cells. A few percent of such T blasts could be shown to carry IgM on their surface when a mixture of T and B lymphocytes was used as responder cells. The immunoglobulin was absent when purified T lymphocytes served as responders. A large proportion of MLC T lymphoblasts could be shown to carry stimulator alloantigens on their surface. These antigens were demonstrated (a) by indirect immunofluorescence using anti-stimulator alloantibody and FITC (fluorescein isothiocyanate Isomer I)-labelled F(ab)2 fragments of rabbit anti-rat Ig; (b) by autoradiography after internal labelling of stimulator cells, which showed the transfer of label from stimulator to responder cells. For biochemical analysis T blasts were restimulated with internally labelled allogeneic or syngeneic stimulator cells, and bound radiolabelled stimulator alloantigens were analysed on SDS-PAGE (sodium lauryl sulphate polyacrylamide gel electrophoresis). The results suggest that intact SD antigens with a molecular weight of 45,000 daltons and LD determinants with a molecular weight of 34,000 daltons derived from stimulator cells are found on MLC T blasts. No evidence of binding of the 27,000-dalton Ia chain to T blasts was found. Possible arrangements of these molecules on the responder blasts is discussed.