Antigen Recognition and the Immune Response

Abstract

The immunogenicity of the small molecule L-tyrosine-p-azobenzenearsonate (RAT) 1 (1, 2) provides an ideal tool for investigating a number of parameters of the immune response. Included among these are the minimum separation between haptenic and carrier determinants required for an anti-hapten antibody response and whether "self-help," the capacity of an immunogenic determinant to cooperate in the humoral response to a second identical determinant, is possible (3). Asymmetric bifunctional molecules consisting of one RAT determinant and one dinitrophenyl (DNP) determinant separated by spacers of various size consistently induced anti-DNP antibody and cellular immunity specific for the RAT group (3). On the other hand, symmetrical bifunctional molecules composed of two RAT determinants separated by the same spacers were unable to provoke either primary or secondary anti-RAT humoral responses (3), although it is well known that the arsonate group is a potent hapten.The spacers used in these studies were flexible chains comprised of one or more units of 6-aminocaproic acid (SAC). Since RAT contains both electropositive (azo) and electronegative (arsonate) centers, the failure of bifunctional RAT compounds with flexible spacers to induce humoral immunity could be ascribed to intramolecular association of the two determinants, in which the basic centers align with the acidic centers in a "deck of cards" geometry (4). Such intramolecular stacking would compromise the bifunctional characters of these molecules. On the other hand, it is also conceivable that both determinants might interact with receptors on the surface of a single irnmunocyte, which would fail to satisfy the requirement for intercellular cooperation.In order to distinguish between these alternative possibilities, bifunctional R A T compounds containing rigid spacers and bifunctional antigens composed of

Mechanisms and prevention of trifluoroacetylation in solid-phase peptide synthesis

“…When proline is the NH2-terminal residue, much more extensive trifluoroacetylation can be expected because of the greater nucleophilicity of the a-imino group which has a pKa about 1 unit higher than an a-amino group. This is why trifluoroacetylation has been most often reported to occur at proline residues (4,5).…”

“…During the assembly of the protected peptide chain, the Boc group is removed at each step under conditions that leave other protecting groups unaffected, most commonly by the use of 50% (vol/vol) trifluoroacetic acid in dichloromethane for [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] min. Acylation of the a-amino group of the growing peptide chain, to give N't-trifluoroacetyl peptides, has been reported on several occasions (4)(5)(6)(7). This potentially general side reaction has serious consequences because the N'"-trifluoroacetyl pep-tides formed are stable to the conditions of solid-phase peptide synthesis, thus lowering the overall yield of the desired product and complicating its purification from the accompanying terminated peptides.…”

ABA‐T Determinant Regulation of Delayed Hypersensitivity

“…It was recently reported that injection of TMA-tyrosine (total molecular weight 344 Daltons) resulted in clonal expansion of specific B-ceUs, again suggesting hapten activity at this end of the molecule. A rigid proline peptide linkage group was, however, required with ABA-T molecules to prevent stacking of the phenyl rings (Bush et al 1972). In addition to the tyrosine 'carrier' and ABA 'hapten' detenninants, investigators have added additional determinants to these molecules via the tyrosine anaino group, resulting in antibody production to the added haptens.…”

“…A great deal of careful research has been carried out with ABA-T and a wide variety of variations on this molecular theme in order to understand the unique immunogenic properties of this small family of molecules (Leskowitz 1963, Borek & Stupp 1965, Jones & Leskowitz 1965a, b, Colloti & Leskowitz 1970, Alkan et al 1971, 1972a, b, Mackler et al 1971, Bush et al 1972, Hanna & Leskowitz 1972, 1973a, b, Becker et al 1975, Bullock et al 1975a, b, c, Brunda & Raffel 1977, Prange et al 1977. A great deal of careful research has been carried out with ABA-T and a wide variety of variations on this molecular theme in order to understand the unique immunogenic properties of this small family of molecules (Leskowitz 1963, Borek & Stupp 1965, Jones & Leskowitz 1965a, b, Colloti & Leskowitz 1970, Alkan et al 1971, 1972a, b, Mackler et al 1971, Bush et al 1972, Hanna & Leskowitz 1972, 1973a, b, Becker et al 1975, Bullock et al 1975a, b, c, Brunda & Raffel 1977, Prange et al 1977.…”