Antigenicity: some molecular aspects

Nonantigenicity and immunologic tolerance: the role of the carrier in the induction of tolerance to the hapten

Treatment of adult mice with dinitrophenyl (DNP) bound to isogeneic serum resulted in a specific inability to respond to DNP after challenge with DNP-keyhole limpet hemocyanin (KLH) in complete Freund's adjuvant. The unresponsiveness to the hapten had all the characteristics of immunologic tolerance: it had a definite induction time; it was transient but could be maintained by additional injections of the tolerogen; it was antigen specific and dose dependent. In addition, the induction of tolerance to DNP is dependent on the nature of the carrier. Two main conclusions can be drawn from these data: DNP conjugates of three homopolymers of lysine were found to be nonimmunogenic in mice, yet tolerogenic. Thus, antigenicity is not necessary to induce tolerance. Among the various carriers tested, isogeneic 7S immunoglobulin (IgG) was found to be the most effective to induce and maintain tolerance to the hapten. This suggests that IgG may have a function other than its usual role as an immunoglobulin.

Antibodies reactive with native lysozyme elicited by a completely synthetic antigen

A synthetic peptide consisting of the aminoacid sequence of residues 64-82 of lysozyme, with alanine replacing cysteine as residue 76, was prepared by the solid-phase technique. Mild reduction followed by reoxidation in air of the deprotected peptide led to the formation of a closed loop containing an intrachain disulfide bond. A conjugate consisting of this "loop" attached to multi-poly(DL-alanyl)-poly(L-lysine) elicited, in rabbits and goats, the formation of antibodies capable of reacting with lysozyme and with the loop peptide prepared from it. These immunological interactions can be inhibited by either lysozyme or the loop peptide, but not by the performic acid-oxidized open-chain peptide. Thus, the antibodies elicited by the completely synthetic antigen show specificity toward the "loop" structure (residues 64-80) of native lysozyme.

Contribution of bone marrow cells and lack of expression of thymocytes in genetic controls of immune responses for two immunopotent regions within poly-(Phe,Glu)-poly-Pro--poly-Lys in inbred mouse strains

Previous cellular studies on the genetic regulation of immunological responsiveness for two immunopotent regions within the branched chain synthetic polypeptide (Phe, G)-Pro--L demonstrated a direct correlation between the number of detectable immunocompetent splenic precursor cells and the response patterns of SJL, DBA/1, and F(1) mice (21). In order to establish the cellular origin(s) of the genetic defect, the present study first demonstrated that thymus and bone marrow cell cooperation was required for (Phe, G)- and Pro--L-specific immune responses. Secondly, limiting dilution experiments, in which several graded and limiting inocula of marrow cells were mixed with a non-limiting number of 10(8) thymocytes and injected into irradiated, syngeneic recipients, indicated that the low responsiveness of the SJL and DBA/1 strains to the (Phe, G) and Pro--L specificities, respectively, could be attributed to a reduced number of precursor cells found in bone marrow. About five times more marrow precursors were detected in SJL mice for Pro--L than for (Phe, G), whereas about five times as many precursor cells were estimated for (Phe, G) as for Pro--L in the DBA/1 strain. These differences are similar to those obtained using spleen cells from unimmunized SJL and DBA/1 donors (21), and indicate that these genetically determined variations in responsiveness can be accounted for by differences in the frequencies of monospecific populations of immunocompetent cells present in bone marrow. In contrast, limiting dilution transfers of thymocytes or thymus-derived cells with an excess of syngeneic marrow cells resulted in equally frequent (Phe, G) and Pro--L responses for both SJL ad DBA/1 strains. This finding in conjunction with the observation that the generation of (Phe, G)- and Pro--L-specific responses were associated in individual recipients injected with limiting inocula of thymocytes indicated that a single population of thymocytes was stimulated by (Phe,G)-Pro--L. Therefore, it is improbable that the thymic population of immunocompetent cells contributes to expression of these genetically controlled defects.

Immune response to chemically modified flagellin. I. Induction of antibody tolerance to flagellin by acetoacetylated derivatives of the protein

Flagellin (mol. wt. 40,000) from S. adelaide organisms was acetoacetylated to varying extents with diketene (acetoacetic anhydride). Chemical studies demonstrated that the amino groups of flagellin were more readily acetoacetylated than the hydroxyl groups. Several antigenic tests revealed that as flagellin was acetoacetylated to increasing extents there was a steady decline in the affinity of the molecule for anti-flagellin antibodies. Loss in antigenic activity following acetoacetylation was not related to the number of acetoacetyl groups attached but was determined by the type of residue substituted. Reactive lysine residues were much less important anti-genically than easily substituted hydroxyl groups. Acetoacetylation very readily destroyed the antibody-forming capacity of flagellin in rats. This fall in immunogenicity was related to the antigenic activity of the preparations. In fact, only a 40% reduction in the antigenic activity of flagellin produced a 90-95% reduction in primary antibody formation. The more heavily acetoacetylated flagellins produced no detectable antibody and, in fact, rendered adult rats tolerant (in terms of antibody formation) to a subsequent challenge of flagellin. Tolerance was induced by acetoacetylated flagellins which had drastically reduced affinities for anti-flagellin antibodies. These results were interpreted as indicating that the affinity of antigen for receptors on cells appears to be of crucial importance in determining whether antibody formation or immunological tolerance (antibody suppression) occurs.

Maternal-fetal interaction and immunological memory

Female rats of the poorly responding, inbred F344 strain were immunized with poly(Glu(52)Lys(33)Tyr(15)) aggregated with methylated bovine serum albumin, and then they were mated. The first and second litters in the F(1) generation and in the F(2) generation showed an enhanced immune response. When poly-lysine was used as the aggregating agent, enhancement occurred in only the first litter of the F(1) generation and in the F(2) generation. In both cases, antigen was transmitted from the immunized female to her offspring, where it localized in the bone marrow and, in a few cases, in the thymus and spleen also. The transplacental passage of antigen is probably the basis for the enhanced antibody response, which is a manifestation of immunological memory.

Antigen recognition and antibody specificity. Carrier specificity and genetic control of anti-dinitrophenyl-oligolysine antibody

The exact specifiicity of anti-DNP antibody produced by Hartley guinea pigs immunized with a series of defined alpha,DNP and epsilon,DNP-oligolysines was studied by fluorescence quenching. All responder animals made anti-DNP antibody which recognized the precise chain length, +/- 1 lysyl residue, of the DNP-oligolysines used to induce the immune response as measured by an increase in binding energy (-DeltaF degrees ) for that antigen. The ability of the immune system to detect the smallest possible change in oligolysine chain length suggests that the anti-hapten antibody-forming cell possesses a highly specific recognition system for carrier conformation. When DNP-oligolysines are incorporated in an adjuvant containing M. tuberculosis H37Rv, both responder and nonresponder produce anti-DNP antibody, but only the responder develops delayed skin sensitivity. In addition to their failure to develop delayed hypersensitivity, nonresponders produced anti-DNP oligolysine antibody which did not show the increase in -DeltaF degrees for the immunizing antigen characteristic of responder antibody. These observations support a local environment hypothesis for antigen recognition at the level of the anti-hapten antibody-forming cell and suggest that the polylysine gene exerts its control at the same cell.

Stimulation in vitro with protein carrier of antibodies against a hapten

Rabbits were immunized both with lysozyme and with dinitrophenylated bovine serum albumin. No antibodies against the dinitrophenyl hapten were produced when cell suspensions of their spleens were exposed in vitro to dinitro-phenyl-ovalbumin, whereas a positive response was obtained with dinitrophenyl-lysozyme. Moreover, when spleen cells from rabbits previously immunized with dinitrophenyl-bovine serum albumin were exposed in vitro to bovine serum albumin alone, they produced antibodies against the dinitrophenyl hapten.