Role of antigenic structure in cell to cell cooperation

Raising antibodies by coupling peptides to PPD and immunizing BCG-sensitized animals

The use of PPD (purified protein derivative of tuberculin) as a carrier has several significant advantages. It provides very powerful T cell help and it gives rise to virtually no antibody response against itself. This is particularly useful if it is intended to go on to make monoclonal antibodies, where the presence of a large amount of anti-carrier antibody is a nuisance! Furthermore, unlike most comparably powerful adjuvant systems, it can be used in man. PPD coupling has been used to raise antibodies to haptens and to raise T cell responses to tumour cells. It is here reported that small peptides coupled to PPD will give rise to good titres of anti-peptide antibody. For peptides that contain no cysteine, coupling has been achieved by attaching succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC) to the alpha-amino group of the peptide and N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) to the PPD and allowing an uncleavable bond to form between them. Data on immunization with the leucotactic nonapeptide of the alpha chain of the complement component C3 and with some oncogene-related peptides have been obtained.

Dichotomy between the T and the B cell epitopes of the synthetic polypeptide (T,G)-A--L

Studies with the well-characterized, synthetic, random-multichain polypeptide poly(LTyr,LGlu)-poly(DLAla)-poly(LLys) (T,G)-A-L) led to the discovery of determinant-specific genetic control of the immune response, as well as to other immunological phenomena. Moreover, the tetrapeptide TyrTyrGluGlu built on the same backbone ("(T-T-G-G)-A--L") was found to represent its major B cell epitope. We have recently shown that for interaction with major histocompatibility complex class II molecules and stimulation of T cells, (T,G)-A--L requires proteolytic processing and the resulting T cell epitopes are close to the N termini of the branched polymer's side chains. Thus, we were interested to elucidate the major T cell epitope of (T,G)-A--L, by using the ordered polypeptides (T-T-G-G)-A--L and (T-G-T-G)-A--L, in which only the two internal amino acids of the tetrapeptide attached to the side chains are switched. We established T cell lines to these antigens, and found that the ordered analog (T-T-G-G-)-A--L, which was defined as the B cell epitope of (T,G)-A--L, did not represent its T cell epitope, whereas (T-G-T-G)-A--L, to which only a minor anti-(T,G)-A--L Ab response was directed, was found to be its major T cell epitope. In addition, there was no cross-reaction between (T-G-T-G)-A--L and (T-T-G-G)-A--L at the T cell level, similar to the lack of cross-reaction of their antibodies. Analysis of the repertoire of the T cell receptors used by these lines revealed that the (T,G)-A--L and the (T-T-G-G)-A--L specific T cell lines were not restricted in their V alpha and V beta TCR usage, whereas the (T-G-T-G)-A--L-specific line was restricted by both V alpha and V beta T cell receptor gene products. This difference might be due to the thymus-independent characteristics previously described for the latter antigen.

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.

Cellular analysis of specificity of antibodies and of delayed type hypersensitivity responses toward some structurally related synthetic antigens: boosting is determined by specificity of T cells

The crossreactivity between the random synthetic polypeptide antigen poly(Tyr,Glu)-poly(DLAla)--poly(Lys) [(T,G)-A--L] and its ordered-sequence analogs (Tyr-Tyr-Glu-Glu)-poly(DLAla)--poly(Lys) [(T-T-G-G)-A--L] and (Tyr-Glu-Tyr-Glu)-poly(DLAla)--poly(Lys) [(T-G-T-G)-A--L] at the level of humoral and cellular responses was studied. For delayed type hypersensitivity responses, (T,G)-A--L-activated T cells could be challenged with the homologous antigen as well as with the ordered analogs. T cells activated by (T-T-G-G)-A--L could be challenged with either the homologous antigen or with (T,G)-A--L but not with (T-G-T-G)-A--L. Similarly, no cross stimulation was observed between (T-G-T-G)-A--L-activated cells and (T-T-G-G)-A--L, whereas (T,G)-A--L could challenge the latter cells to mediate significant responses. Similar but not identical cross reactions were observed when primed spleen cells or lymph nodes were transferred to irradiated recipients that were boosted for the production of antibodies. In contrast to observations at the level of cellular responses, (T-G-T-G)-A--L-primed spleen or lymph node cells could not be boosted with (T,G)-A--L for the production of detectable amounts of antibodies, although boosting with the homologous antigen resulted in significant levels of (T-G-T-G)-A--L-specific antibodies. Transfer experiments in which mixtures of T and B cells, each primed to a different ordered polypeptide antigen, were injected into irradiated recipients showed that successful cooperation occurs provided that the boost is given with the T-cell-specific antigen. The antibodies produced were specific to the antigen used for B-cell priming. The T-cell-B-cell collaboration probably occurs through specific determinants that are shared between the two antigens in which the ordered peptides are attached to the same multichain polymer and that are recognized by both the T and the B cells.

Antigen-reactive T clones. III. Low responder antigen-presenting cells function effectively to present antigen to selected T cell clones derived from (High Responder x Low Responder)F1 mice

Long-term-cultured poly(Tyr, Glu)-poly-D,L,-Ala-poly-Lys [(T,G)-A--L]-reactive T cells and clones derived from (high responder x low responder)F1 [(C57BL/6 x A/J)F1] mice were shown to recognize (T,G)-A--L presented by cells from low responder strain A/J mice. The antigen-presenting determinant(s) that allowed recognition of (T,G)-A--L by such T cell clones was controlled by the I-A subregion of the major histocompatibility complex. These results suggest that there is no functional defect in the ability of low responder Ir gene products (I-A antigens) to associate with (T,G)-A--L for effective recognition by T cells. Although these results might tentatively be interpreted to suggest that Ir gene-controlled low responsiveness is due to the inability of the T cell to recognize the association between (T,G)-A--L and low responder I-A gene products, it is similarly possible that there might be a defect in the functional capabilities of low responder antigen-presenting cells to effectively process (T,G)-A--L into immunodominant epitopes.

Change in specificity of antibodies to a random synthetic branched polypeptide in mice tolerant to its ordered analogs

The crossreactivity between the random synthetic polypeptide antigen, (Tyr,Glu)-poly(DLAla)- -poly(Lys), and its ordered sequence analogs, (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(Lys) and (Tyr-Glu-Tyr-Glu)-poly(DLAla)- -poly(Lys), has been studied on the level of tolerance induction. Induction of tolerance to the random (Tyr,Glu)-poly(DLAla)- -poly(Lys) affected the response of the tolerant mice to the homologous antigen as well as to (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(Lys), which was shown previously to represent the major determinant of (Tyr,Glu)-poly(DLAla)- -poly(Lys). In contrast, these mice responded with high antibody titers to the hardly crossreacting (Tyr-Glu-Tyr-Glu)-poly(DLAla)- -poly(Lys). Mice tolerant to the ordered peptide antigen (Tyr-Glu-Tyr-Glu)-poly(DLAla)- -poly(Lys) did not respond to the homologous polypeptide; however, their immune response to either (Tyr-Glu)-poly(DLAla)- -poly(Lys) or (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(Lys) was not affected. Mice that were tolerant to (Tyr-Tyr-Glu-Glu)-poly(DLAla)- -poly(Lys) responded well to (Tyr-Glu-Tyr-Glu)-poly(DLAla)- -poly(Lys). Furthermore, these mice produced high antibody titers after immunization with the random (Tyr,Glu)-poly(DLAla)- -poly(Lys). However, the antibodies produced were not specific to the major determinant of (Tyr,Glu)-poly(DLAla)- -poly(Lys), namely, Tyr-Tyr-Glu-Glu, but were directed to minor determinants of the random polypeptide, including Tyr-Glu-Tyr-Glu, which are not immunopotent when nontolerant mice are immunized with (Tyr,Glu)-poly(DLAla)- -poly(Lys). Thus, whereas antigenic specificity reflects itself also at the level of tolerance induction, the animals that had been made tolerant are capable of responding to previously silent antigenic determinants.

The mode of interaction with macrophages of two ordered synthetic polypeptides which differ in their thymus dependency

The mode of interaction with macrophages of two ordered synthetic polypeptides (Tyr-Tyr-Glu-Glu)-poly(DLAla)--poly(Lys), (T-T-G-G)-A--L, and (Tyr-Glu-Tyr-Glu)-poly(DLAla)--poly(Lys), (T-G-T-G)-A--L, which differ in their requirements for T-B cell co-operation in the process of antibody production, was compared. The binding of the two radiolabelled antigens to the surface of peritoneal adherent cells, their uptake by the cells and the rate of their degradation were investigated. Macrophages were found to be capable of degrading both poly-peptides with the same efficiency. (T-G-T-G)-A--L, the antigen which is less T-dependent, was bound to macrophage surfaces more readily than (T-T-G-G)-A--L, the T-dependent antigen, however, its uptake by the cells was found to be lower. Thus, (T-G-T-G)-A--L remains for a longer period in the form of a membrane bound polyvalent antigen.

Cellular and genetic control of antibody responses in vitro. II. Ir gene control of primary IgM responses to trinitrophenyl conjugates of poly-L-(Tyr,Glu)-poly-D,L-Ala--poly-L-Lys and poly-L-(His,Glu)-poly-D,L-Ala--poly-L-Lys

The in vitro primary IgM anti-hapten responses to trinitrophenyl (TNP) conjugates of poly-L-(Tyr,Glu)-poly-D,L-Ala-poly-L-Lys (T,G)-A--L and poly-L(His,Glu)-poly-D,L-Ala--poly-L-Lys (H,G)-A--L were shown to be T-cell dependent and under autosomal dominant H-2-linked Ir gene control which mapped within the K or I-A regions of the H-2 complex. The in vitro response to TNP-keyhole limpet hemocyanin, while T-dependent, was not under demonstrable genetic control. The genes governing the in vitro primary IgM anti-hapten responses to TNP-(T,G)-A--L and TNP-(H,G)-A--L resemble the Ir genes controlling the in vivo secondary IgG responses to (T,G)-A--L and (H,G)-A--L in that they are autosomal dominant, map identically within the H-2 complex, and have identical responder and nonresponder haplotypes. It is concluded that Ir genes can govern the ability to generate an IgM response upon initial exposure to antigen.