Contribution of different cell types to the genetic control of immune responses as a function of the chemical nature of the polymeric side chains (poly-L-prolyl and poly-DL-alanyl) of synthetic immunogens

Ia-antigen-T-cell interactions for a thymus-independent antigen composed of D amino acids

Synthetic polypeptide antigens of L amino acids, although bearing repeating sequences, are thymus-dependent (L-TD), whereas the same polymers composed of D amino acids are thymus-independent (D-TI), probably due to a slower rate of metabolism. Yet we found that lymph-node cells of BALB/c mice immunized with D-TI proliferate in response to it in vitro. To follow T-cell activation by D-TI, we established T-cell hybridomas to D-TI and to its analog composed of L isomers, L-TD, for comparison. The T-cell hybridomas express membrane alpha/beta T-cell receptors and secrete interleukin 2 upon stimulation with the respective antigen. In addition, D-TI-specific hybridomas are stimulated, to a lesser extent, by the L-TD antigen, whereas only some L-TD-specific hybridomas recognize D-TI. Moreover, biotinylated analogs of D-TI and L-TD bind to splenic antigen-presenting cells (APCs) from BALB/c mice. Binding is inhibited by an excess of nonbiotinylated L-TD, and by an excess of a peptide comprising residues 259-271 of the human acetylcholine receptor alpha subunit, which binds to I-Ad and I-Ed molecules without prior processing. Analysis of APC lysates following incubation of the APCs with biotinylated D-TI and L-TD reveals that the biotinylated antigen moiety is associated with Ia molecules. D-TI and L-TD bind to Ia molecules on intact APCs with similar KD values, 5 x 10(-8) M and 3 x 10(-8) M, respectively. However, D-TI has faster kinetics of binding than L-TD, probably due to different processing requirements. Hence, we have demonstrated a major histocompatibility complex class II-mediated T-cell response to a thymus-independent antigen.

Splenic B cells function as immunogenic antigen-presenting cells for the induction of effector T cells

Previous studies performed in our laboratory have revealed that an ordered, sequential, tricellular interaction is obligatory for the antigen-driven induction of a specific effector memory T cell. Thus, it was found that antigen-pulsed peritoneal macrophages signal, in spleen cells, the generation of antigen-specific initiator lymphocytes. These lymphocytes, following injection to syngeneic recipients, recruit, in the draining lymph nodes, "virgin" antigen-reactive T lymphocytes. Although the nature of the first and last cell in the interacting sequence was well characterized, the identity of the intermediary initiator splenic cell was obscure. Studies were carried out to characterize the nature of the splenic initiator cells. It was found that spleen cells from nu/nu, adult thymectomized and neonatal thymectomized, or spleen cells from normal donors which had been subjected to cytolysis using anti-Thy-1.2 antibodies in the presence of complement, did generate, following interaction with keyhole limpet hemocyanin (KLH)-fed macrophages, specific initiator cells. Carrageenan impairment of spleen macrophages did not affect the generation of initiator cells, nor did the depletion of dendritic cells from the spleen. On the other hand highly enriched B cell, but not highly enriched T cell populations, when seeded on KLH-pulsed macrophages, generated antigen-specific initiators, which, in vivo, recruited antigen-reactive T cells. It thus appeared that B lymphocytes can function as intermediary obligatory antigen-presenting cells and actively transfer immunogenic signals from peritoneal antigen-presenting cells to T lymphocytes. These findings may therefore suggest that antigen-specific B cells do not function solely as antibody-producing cells, but, once activated by macrophages, may control the induction and differentiation of some antigen-reactive T cell subsets. Thus, one can view the B cell as an important regulatory cell of both cellular and humoral immune functions. The significance of this observation with regard to Ir gene control at the level of B lymphocytes is discussed.

Antiviral response elicited by a completely synthetic antigen with built-in adjuvanticity

In a previous study we demonstrated that antiviral response against the coliphage MS-2 can be elicited by immunization with a synthetic antigen consisting of a conjugate (P2-A -- L) of a synthetic fragment (P2) of the virus coat protein attached to a synthetic polymeric carrier. The antiviral response was induced when the antigen was administered in complete Freund's adjuvant or when it was administered in incomplete adjuvant, provided that a peptidoglycan was covalently attached to it. In the present study we demonstrate the adjuvant effect of N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP) in this system. Immunization with a mixture of MDP and P2-A -- L brought about only slight enhancement in the titer of neutralizing antibodies, as compared to the immunization with P2-A -- L in saline. The best results were achieved when the MDP was chemically conjugated to P2-A -- L. This completely synthetic material, when administered in aqueous solution, yielded highly inactivating antiserum with a titer similar to that obtained with complete Freund's adjuvant in the absence of MDP. MDP-P2-A -- L elicited also a humoral immune response to MDP, but with much lower titer than that induced by complete Freund's adjuvant containing P2-A -- L only. It was also observed that the capacity of MDP-P2-A -- L to increase resistance against infection was more than a 100-fold greater than that of unconjugated MDP.

The role of H-2 linked genes in helper T-cell function. IV. Importance of T-cell genotype and host environment in I-region and Ir gene expression

We have studied the properties of helper T cells specific for sheep erythrocytes (SRBC), keyhole limpet hemocyanin (KLH), or poly-L-(Tyr,Glu)-poly-DL-Ala-poly-L-Lys [(T,G)-A--L]. These T cells differentiated and were primed in vivo in irradiation chimeras constructed of various combinations of F1 and parental bone marrow donors and irradiated recipients. Primed T cells were then tested for helper activity in the in vitro response of B cells and macrophages (Mphi) of parental or F1 origin to the hapten trinitrophenol coupled to the priming antigen. When testing either SRBC or KLH-specific T cells of parental H-2 type which had differentiated in F1 hosts, we found that they cooperated equally well with B cells and Mphi of either parental H-2 type. On the other hand, when testing F1 T cells which had differentiated in parental hosts, we found that they cooperated well only with B cells and Mphi which had the K-IA region type of the parental host. In similar experiments we found that (T,G)-A--L-specific T cells of low responder H-2 type which had differentiated in (high responder X low responder) F1 hosts induced high responses in high responder B cells and Mphi (T,G)-A--L-specific F1 T cells which differentiated in high responder but not those which differentiated in low responder hosts induced high responses in high responder B cells and Mphi. Low responder B cells and Mphi yielded low responses in all cases regardless of the source of (T,G)-A--L-specific T cells with what they were tested. Our results support the conclusion that I-region and Ir genes function via their expression in B cells and Mphi and in the host environment during helper T-cell differentiation, but not, at least under the conditions of these experiments, via their expression in the helper T cell itself. These findings place constraints upon models which attempt to explain the apparent dual recognition of antigen and I-region gene products by helper T cells.

The role of H-2-linked genes in helper T-cell function. III. Expression of immune response genes for trinitrophenyl conjugates of poly-L(Tyr, Glu)-poly-D,L-Ala--poly-L-Lys in B cells and macrophages

Using lymph node T cells from poly-L(Tyr,Glu)-poly-D,L-Ala--poly-L-Lys[(TG)-A--L]-primed animals and B cells from animals primed with trinitrophenylated (TNP) protein or lipopolysaccharide, we have obtained anti-TNP-(TG)-A--L direct plaque-forming responses in vitro. Response to this antigen was shown to be controlled by the H-2 haplotype of the animal studied. The strain distribution of in vitro response was very similar to that previously reported by others for in vivo secondary IgG responses to (TG)-A--L. We investigated the cell types expressing the Ir gene(s) for (TG)-A--L in our cultures. F1, high responder x low responder mice were primed with (TG)-A--L. Their T cells were active in stimulating anti-TNP-(TG)-A--L responses of high responder but not low responder B cells and macrophages (MPHI), even though both preparations of B cells and Mphi were obtained from mice congenic at H-2 with one of the parents of the F1. For three low responder strains tested, of the H-2h2, H-2k, and H-2f haplotypes, the anti-TNP-(TG)-A--L response of low responder B cells and Mphis in the presence of high responder, F1 T cells could not be improved by the addition of high responder, antigen-bearing Mphis to the cultures. In one strain of the H-2a haplotype, it was shown that neither the B cells nor Mphis could be functional in anti-TNP-(TG)-A--L responses. Our results therefore suggested the Ir genes for anti-TNP-(TG)-A--L responses were expressed at least in B cells in all the low responder strains we studied, and, in mice of the H-2a haplotype, in Mphis too.

In vitro studies on H-2 linked unresponsiveness. 1. Normal helper cells to (T,G)-A-L and GAT in low and non-responder mice

Lymphoid cells from unprimed high responder (C57BL/10) and low responder mice (B10.Br, B10.A, CBA) to (T,G)-A-L and high responder (B10, B10.A) and non-responder (B10.G, DBA/I) mice to GAT can be induced to form antigen specific T-helper cells in vitro under identical culture conditions. The helper cells induced from high and low or non-responder mice appear to be identical in efficiency, antigen concentration requirement for induction and induction kinetics.

Antiviral effect on MS-2 coliphage obtained with a synthetic antigen

The coat protein of bacteriophage MS-2 was cleaved with cyanogen bromide to yield three fragments, possessing the sequence 1-88 (P1), 89-108 (P2), and 109-129 (P3), respectively. The mixture of peptides P2 and P3, which could not be separated, was found capable of inhibiting the neutralization of the phage by antiserum to the whole MS-2. The peptides corresponding to P2 and P3 were therefore synthesized. The synthetic P3 had no capacity to interfere with neutralization of MS-2, not did its macromolecular conjugate with multichain poly(DL-alanine) elicit neutralizing antibodies. On the other hand, the synthetic P2 was very efficient in inhibiting the inactivation of the phage by the antiserum against phage. Furthermore, a synthetic antigen prepared by attachment of P2 to multichain poly(alanine) incuded antiserum in rabbits that was capable of neutralizing MS-2 activity almost as efficiently as the antiserum prepared against the intact coat protein. This inactivation is specific, because it can, in turn, be totally inhibited by P2 peptide.

Role of antigenic structure in cell to cell cooperation

Two synthetic polypeptides which differ only in the order of amino acids in their NH2-terminal side chains, namely, (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(LLys) and (Tyr-Glu-Try-Glu)-poly(DLAla)- -poly(LLys), were found to be under different genetic control. By three different in vivo systems for thymus-derived cell depletion, it was demonstrated that (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(LLys), which represents the random poly(Tyr,Glu)-poly(DLAla)- -poly(Lys) in the pattern of immune responses and in the quality of antibodies they elicit, is thymus-dependent whereas (Tyr-Glu-Tyr-Glu)-poly(DLAla)-poly(LLys) does not require thymus-derived cell help for efficient antibody production. Therefore, the two ordered polypeptides which are similar chemically differ in parameters, not yet determined, which affect their capability to trigger bone marrow-derived cells.

Analysis of the role of different cell types in the genetic regulation of antibody production to the thymus-independent synthetic polypeptide poly (DTyr, DGlu)-poly (DPro)--poly (DLys)

The immune response potential of mice to the thymus-independent synthetic polypeptide poly (DTyr, DGlu)-poly(DPro)--poly(DLys)[D(T,G)-Pro--L] is genetically regulated. The defect in the ability of low responder mice to mount an immune response to this antigen appears to be expressed in their B cell population since the presence of thymocytes, or addition of "educated T cells" or supernatant of T cells after stimulation with the antigen neither enhanced, nor suppressed the level of antibodies produced in both low and high responder mice. Low responsiveness could not be enhanced either by stimulation of macrophages or by injection of poly(A) - poly(U) in contrast to the significant effect of these agents on low responses to the thymus-dependent poly(LTyr, LGlu)-poly(LPro)--poly(LLys) [L(T,G)-Pro--L]. These results suggest that macrophages do not participate in the limiting step, or are not involved at all, in antibody production towards the thymus-independent polypeptide. The antibodies produced in response to D(T,G)-Pro--L were found to be mainly of the 7 S class. T cells are not required for the production of mercaptoethanol resistant antibodies to this immunogen since they were found in intact mice as well as in T cell depleted animals.

Varied effects of polyadenylic-polyuridylic acid on immune responses

The effect of the double-stranded synthetic polynucleotide, poly(A).poly(U), on the immune response of inbred mouse strains to multichain synthetic polypeptides was studied. Poly(A).poly(U) did not affect immune responses controlled by H-2 linked genes. Thus, when either (T,G)-A- -L or (Phe,G)-A--L were injected into high or low responder mice followed by administration of poly(A).poly(U) 24 h after immunization, no increase in the antibody titers was observed. In contrast, poly(A).poly(U) increased significantly the response to polyproline, which is controlled by a non H-2 linked gene, in low responder mice. However, the polyribonucleotide had no effect on the antibody titers of the SJL mice, the high responders to multichain polyproline. When poly(A).poly(U) was injected into DBA/1 mice following immunization with (Phe,G)-Pro- -L, the polynucleotide enhanced the low response to the Pro- -l region at the expense of the anti (Phe,G) response which is normally high in this mouse strain. In this case poly(A).poly(U) caused an intramolecular antigenic competition. The general conclusion of this study is that the chemical nature of the antigenic determinant plays an important role in determining the type of influence exerted by poly(A).poly(U).

Comparison of the immune response potential of newborn mice to T-dependent and T-independent synthetic polypeptides

Newborn mice do not, in general, produce antibodies during the 1st week of life; this inability to respond immunologically has been attributed to lack of functional macrophages and T cells. To determine whether B cells of newborn mice are functionally mature and therefore capable of producing antibodies to thymus (T) independent antigens, the response of 1-9-day-old C3H/HeJ mice injected with a thymus-independent polypeptide, poly(DTyr,DGlu)-polyDPro- -polyDLys was compared to that of their littermates injected with a thymus-dependent immunogen, poly(LTyr,LGlu)-polyLPro- -polyLLys. No antibodies were detected in 1- or 2-day-old mice immunized with the T-dependent antigen, as revealed by haemagglutination and haemolytic plaque-forming cell assays, performed 6 days after injection of the antigen. Injection of 3-day-old animals with the thymus-dependent immunogen resulted in significant immune responses which increased with age. In contrast, 1- and 2-day-old mice responded to the T-independent immunogen with high antibody levels, however, in 3-day-old injected mice, the levels were lower. When 3-day-old nude mice were injected with this antigen, no decrease in the immune response was observed. Thus, newborn mice respond immunologically to a thymus-independent antigen injected at the first 2 days after birth and the antibody levels decrease with maturation of the thymus.

Lymphocyte surface immunoglobulins

Immunoglobulins have been isolated from the surface of B (bone marrow-derived) and T (thymus-derived) lymphocytes. Two types of membrane immunoglobulin occur on B lymphocytes; one type resembles the 200,000-dalton subunit of IgM, the second possesses a heavy chain electrophoretically distinct from mu chain and does not correspond to any of the known classes of mouse immunoglobulins. It might correspond to human sigma chain. T lymphocytes possess only one type of surface immunoglobulin. This molecule has a mass of approximately 200,000 daltons and contains light chains and heavy chains similar to, but not identical to, mu chains. Evidence now exists that surface IgM-like immunoglobulins of B lymphocytes and T lymphocytes activated to certain antigens can bind specifically to antigen. These observations suggest that surface immunoglobulin functions as a receptor for antigen on B cells and at least on some T cells. The mechanisms by which combination of antigen with surface immunoglobulin initiate differentiation remain to be determined.

Transplantation behavior of A.TH and A.TL T-cell lymphomas in congenic resistant and hybrid strains

Seven spontaneously arising T-cell lymphomas originating in A.TH or A.TL mice, which are congenic for the immune response gene (I) chromosomal segment were described. When transplanted into partner strains which were incompatible at the I region, the tumors were rapidly rejected. Rejection was proposed to be due to the presence of antigens controlled by I-region genes.

The genetic control of the antibody response in inbred rats

The antibody response of genetically inbred rats to poly(Glu52Lys33Tyr15) is controlled by a complex polygenic system which includes at least two autosomal genes and a sex influence, which may also be genetically determined. The genetic control of the quantity, binding constants, and specificity of the antibody formed linked to the major histocompatibility locus. Factors other than the major genetic ones and the sex influence also affect the quantity of antibody formed, since animals of the same genotype can make significantly different amounts of antibody, depending upon the crosses by which they acquire the major histocompatibility alleles. After immunization with poly(Glu52Lys33Tyr15) the low responders make fewer antibody-producing cells, are not capable of mounting a delayed hypersensitivity reaction to the polypeptide and appear to be deficient in their ability to produce the specific IgM antibody. Immunization of the low responders with antigen aggregated with methylated bovine serum albumin enhances the quantity of antibody formed, increases the binding constants and crossreactivity of the antibody and enhances the delayed hypersensitivity response. In contrast to the findings with the L-amino acid polypeptide, there does not appear to be any genetic control over the antibody response to the D-amino acid enantiomorph poly(DGlu52DLys33DTyr15), which is minimal in all strains.

Genetic control of immune response. The dose of antigen given in aqueous solution is critical in determining which mouse strain is high responder to poly(LTyr, LGlu)-poly(LPro)--poly(LLys)

Antibody response to different doses of (T,G)-Pro--L, given in aqueous solution, was investigated in the high responder SJL and low responder DBA/1 strains by measuring hemolytic plaque-forming cells (PFC) in the spleens as well as hemagglutination titers in the sera. The gene responsible for the difference between the two strains in the response to this antigen, given in complete Freund's adjuvant, has been previously denoted Ir-3. This gene is not linked to the major histocompatibility locus. In the response to the optimal dose (1 mug) of antigen, no difference could be shown between the strains. The peak of the response and the numbers of direct and indirect PFC were similar in both strains in the primary and secondary response. After injection of higher doses (10-100 mug) of antigen, both the direct and indirect PFC responses were lower in the low responder than in the high responder strain. Moreover, the peak of the response occurred earlier in the high responder strain in the primary response to the 10 mu dose of antigen. After administration of a suboptimal dose (0.02 mug) of antigen, the low responder strain produced in the primary response 4-20 times more indirect plaques than the high responder strain. Also the number of direct plaques was higher in the low responder than in the high responder strain. The serum antibody responses to the optimal and higher doses of antigen were parallel to the PFC responses. From inhibition of PFC with free antigen, it was concluded that a similar proportion of cells was producing high and low affinity antibodies to (T,G)-Pro--L in both strains. High and low zone tolerance could be induced in the two strains with (T,G)-Pro--L, but no difference could be shown between the strains. It is suggested that the Ir-3 gene plays a role in the regulation of the balance stimulation and suppression according to the dose of antigen given.

The possible role of i region determined cell surface molecules in the regulation of immune responses

An hypothetical model has been presented by which I region determined cell surface molecules (Ia antigens) mediate the collaboration between T cells and B cells leading to control of the humoral immune response. The model proposes an analogy between Ia antigens and the constant regions of Ig chains. The absolute requirements of this model are: a) On the B cell the Ia antigen is closely associated with the Fc receptor; b) On the T cell the Ia antigen is closely associated with the product of a linked variable region gene which functions as a specific T cell binding site; and c) The interaction between the T cell Ia molecule and its B cell counterpart leads to B cell activation. By the proposed interactive model no additional Ir gene products are required to explain current concepts of Ir gene function. The experimental evidence from our own laboratory and elsewhere upon which this model is based has been reviewed and a variety of consequences and predictions of the model have been examined. There are numerous aspects of the model which, because of a lack of hard data, are open to alternative explanations. The possible usefulness of this model should lie in its ability to suggest further experiments to elucidate the mechanism of B cell activation and control of the immune response.

Genetic control of the antibody response to poly-L(Tyr,Glu)-poly-D,L-Ala--poly-L-Lys in C3H--CWB tetraparental mice

In order to further delineate the mechanisms underlying genetic unresponsiveness, tetraparental mice were constructed from immune response-1A gene high responder and low responder parental genotypes, then were immunized with poly-L-(Tyr,Glu)-poly-D,L-Ala--poly-L-Lys ((T,G)-A--L). An analysis of the total serum allotype mixture and of the antigen-binding capacity of the separated allotypes demonstrated that in the milieu of a tetraparental mouse, both high and low responder B cells could be stimulated equally to produce identical high titered anti-(T,G)-A--L responses. Furthermore, these studies show that effective stimulation could occur across a histocompatibility disparity.

Comparative analysis of antigen-binding T cells in genetic high and low responder mice

[(125)I](T,G)-A--L-binding T cells have been studied in mice whose ability to mount an immune response to (T,G)-A--L is under control of the H-2-linked Ir-1A gene. Nonimmunized high and low responder mice have approximately the same frequency of T-ABC. Following immunization, T-ABC proliferated only in high responders, but not in low responders, indicating expression of Ir-1A in T cells. When, for comparison, [(125)I]arsanyl-mouse serum albumin binding B and T cells were investigated in mice whose antibody response to the hapten arsanyl is controlled by an allotype-linked Ir gene, it was found that following immunization the number of B-ABC increased only in high responders. In contrast, T-ABC proliferated to the same extent in both high and low responders, suggesting exclusive expression of the allotype-linked Ir gene in the B-cell line. Preliminary studies indicate that anti-Ia sera inhibit neither B-ABC nor T-ABC.

Evidence for the expression of Ia (H-2-associated) antigens on thymus-derived lymphocytes

We have demonstrated in an anti-Ia serum the presence of specific antibodies reacting with T cells, as well as with B cells, using a highly sensitive dye exclusion test. This antiserum reacts with both spleen and lymph node in a characteristic biphasic titration curve killing up to 70% of these cells. It also reacts with cortisone-resistant thymocytes. The A.TH-alpha-A.TL serum can be absorbed with spleen, lymph node, cortisone-resistant thymus, or normal thymus cells. Further in vivo absorptions in BALB/c nude cannot remove all of the cytotoxic activity for normal BALB lymph node lymphocytes, while completely removing the activity for nude cells. A Thy-1 positive cell line derived from a C57Br leukemia is reactive with this anti-Ia serum.

The genetic control of T cell-meditated immunity. I. Characterization of a mouse strain whose low responsiveness is inherited as a recessive trait

The aim of the experiments was to find a T cell-mediated cytotoxic reaction where genetically determined low responsiveness is under the control of recessive genes. The T cell-mediated immune response to DBA/2 mastocytoma cells P 815-X2 in different inbred strains, F1 hybrids and congenic resistant strains of mice was determined using the ⁵¹Cr-release method. Two tyes of low responsiveness were found. The first already well documented type is characterized by dominance of low responsiveness in genetical analysis. It is due to tolerance because of the identity of the H-2 linked specificities of the recipient and of DBA/2 (H-2^d) mice from which the tumour is derived. The second and new type of low responsiveness in T cell-mediated immunity was found in DBA/1 mice. In this strain low responsiveness is inherited as a recessive trait. The cytotoxic response of DBA/1J mice against the C57B1/6 lymphoma EL 4 is normal. Thus, their low responsiveness is restricted to a limited number of membrane determinants.

Genetic control of the immune response: in vitro stimulation of lymphocytes by (T,G)-A--L, (H,G)-A--L, and (Phe,G)-A--L

In vitro antigen-induced tritiated thymidine uptake has been used to study the response of sensitized lymphocytes to (T,G)-A--L, (H,G)-A--L, and (Phe,G)-A--L in responder and nonresponder strains of mice. The reaction is T-cell and macrophage dependent. Highly purified T cells (91% Thy 1.2 positive) are also responsive, suggesting that this in vitro lymphocyte transformation system is not B-cell dependent. Lymphocytes from high and low responder mice stimulated in vitro react as responders and nonresponders in a pattern identical to that seen with in vivo immunization. Stimulation occurs only if soluble antigen is added at physiological temperatures; antigen exposure at 4 degrees C followed by washing and incubation at 37 degrees C fails to induce lymphocyte transformation. Stimulation is specific for the immunizing antigen and does not exhibit the serologic cross-reactivity which is characteristic of these three antigens and their respective antisera. The reaction can be inhibited by anti-H-2 sera but not by anti-immunoglobulin sera. The anti-immunoglobulin sera did, however, inhibit lipopolysaccharide or pokeweed mitogen stimulation. These results suggest that the Ir-1A gene(s) are expressed in T cells, and that there are fundamental physiologic differences between T- and B-cell antigen recognition.

Antigen-specific thymus cell factors in the genetic control of the immune response to poly-(tyrosyl, glutamyl)-poly-D, L-alanyl--poly-lysyl

The genetic control of the antibody response to a synthetic polypeptide antigen designated poly-L(Tyr, Glu)-poly-D,L-Ala--poly-L-Lys [(T, G)-A--L] has been studied in congenic high responder C3H.SW (H-2(b)) and low responder C3H/HeJ (H-2(k)) strains of mice. This response is controlled by the Ir-1 gene and is H-2 linked. The method employed was to study the ability of specifically primed or "educated" T cells of each strain to produce cooperative factors for (T, G)-A--L in vitro. Such factors have been shown to be capable of replacing the requirement for T cells in the thymus-dependent antibody response to (T, G)-A--L in vivo. The T-cell factors produced were tested for their ability to cooperate with B cells of either high or low responder origin by transfer together with bone marrow cells and (T, G)-A--L into heavily irradiated, syngeneic (for bone marrow donor) recipients. Direct anti-(T, G)-A--L plaque-forming cells were measured later in the spleens of the recipients. The results showed that (a) educated T cells of both high and low responder origin produced active cooperative factors to (T, G)-A--L, and no differences between the strains in respect to production of T-cell factors could be demonstrated; and (b) such factors, whether of high or low responder origin, cooperated efficiently with B cells of high responder origin only, and hardly at all with B cells of low responder origin. The conclusion was drawn that the cellular difference between the two strains lies in the responsiveness of their B cells to specific signals or stimuli received from T cells. As far as could be discerned by the methods used, no T-cell defect existed in low responder mice and the expression of the controlling Ir-1 gene was solely at the level of the B cells in this case.

The role of the thymus in a genetically controlled defect of the immune response at the carrier level

The genetic control of the immune response may be either specific for antigenic carrier or for determinant. We describe here results which show that a carrier-dependent strain defect in immune response is reflected in thymocytes. These results are in agreement with our hypothesis that the genetic defect in the immune response is reflected in thymocytes when the poor response is at the carrier level, whereas it is expressed in the bone marrow population when the low responsiveness is strictly at the determinant level. SWR mice are low responders to multichain polyproline. Furthermore, this mouse strain does not produce antibodies to determinants such as peptides of phenylalanine and glutamic acid (Phe,Glu) or to the loop peptide of lysozyme when attached to polyproline, although they respond well to the same antigenic determinants when conjugated to multichain poly(DL-alanine). Transfer experiments in which irradiated SWR recipients were injected with excess of DBA/1 thymocytes (which do not exhibit a defect in response to polyproline) mixed with graded numbers of SWR marrow cells, prior to immunization with poly(Tyr,Glu)-poly(Pro)--poly(Lys), have indicated that the poor response potential of SWR mice to polyproline is not reflected in their bone marrow cells. Allogeneic transfers in which mixtures of thymocytes and marrow cells from high and low responders were injected into irradiated mice, followed by immunization with poly(Tyr,Glu)-poly(Pro)--poly(Lys) or poly(Phe,Glu)-poly(Pro)--poly(Lys) have demonstrated a clear defect in the thymus derived population of SWR mice when the response potential to polyproline and to determinants attached to it was tested.

Thymus independence of a collagen-like synthetic polypeptide and of collagen, and the need for thymus and bone marrow-cell cooperation in the immune response to gelatin

Several inbred mouse strains were screened for their ability to respond to the ordered periodic collagen-like polymer (Pro-Gly-Pro)(n), to the random copolymer (Pro(66), Gly(34))(n), to the protein conjugate Pro-Gly-Pro-ovalbumin, to rat tail tendon collagen, rat tail tendon gelatin, and to Ascaris cuticle collagen. Differences were obtained in the magnitude of the antibody titers towards the above immunogens among the strains tested. The level of the response to the ordered polymer (Pro-Gly-Pro)(n) was not similar to that towards the random (Pro(66), Gly(34))(n), confirming differences in the antigenic determinants of the two immunogens. The role of the thymus in the immune response to (Pro-Gly-Pro)(n) and (Pro(66), Gly(34))(n) as well as to two collagens and gelatin, was studied in order to find out a possible correlation with the structural features of the immunogens. Heavily irradiated recipients were injected with syngeneic thymocytes, marrow cells, or a mixture of both cell populations and were immunized with the above-mentioned antigens. An efficient immune response to the ordered collagen-like (Pro-Gly-Pro)(n) was obtained in the absence of transferred thymocytes. The thymus independence of (Pro-Gly-Pro)(n) was confirmed when thymectomized irradiated mice were used as recipients. In contrast with these results, cooperation between thymus and marrow cells was necessary in order to elicit an immune response to (Pro(56), Gly(34))(n). Similarly, the immune response to the triple helical collagen was found to be independent of the thymus, whereas for an effective response to its denatured product, gelatin, thymus cells were required. These findings indicate that a unique three-dimensional structure of immunogens possessing repeating antigenic determinants plays an important role in determining the need for cell to cell interaction in order to elicit an antibody response.