IR GENE COMPLEMENTATION IN THE MURINE T-LYMPHOCYTE PROLIFERATIVE RESPONSE

Abstract

ABSTRACT The immune responses to poly(Glu 55 Lys 36 Phe 9 ) [GLO 9 ], poly(Glu 57 Lys 38 Tyr 5 ) [GLT 5 ], and pigeon cytochrome c . are controlled by two major histocompatibility (MHC)-linked immune response (Ir) genes, one mapping in the I-A subregion, the other in the I-E/C subregion. In the case of pigeon cytochrome c the major antigenic determinant has been localized through cross-stimulation experiments involving species variants and cyanogen bromide-cleavage fragments of the molecule. The determinant was shown to be composed of at least three amino acids, Ile-3, Gln-100 and Lys-104, which lie adjacent to one another in a linear array on the back surface of the molecule. Therefore, two complementing Ir genes control the response to a single antigenic determinant. Furthermore, in one cross-reaction, that obtained with tobacco hornworm moth cytochrome c , the stimulation was greater than that achieved with the immunogen, thus demonstrating for the first time a heteroclitic T cell response. The cellular sites of expression of these complementing Ir genes has been examined in several ways. Re-constitution of lethally irradiated high responder F 1 mice with a mixture of bone marrow cells from both low responder parental strains failed to generate chimeras which could respond to GLO 9 . This suggested that at least one cell type involved in the immune response had to express both gene products. That the antigen-presenting cell (APC) was one such cell type was demonstrated by presenting GLO 9 to primed F 1 T cells on nonimmune spleen cells. Only high responder F 1 spleen cells could present; low responder parental spleen cells, possessing only one of the two high responder alleles, failed to present even when both parental types were added together. However, possession of a high responder genotype was not always sufficient to generate a response. In the case of GLT 5 , gene dosage effects appeared to prevent the B10 and B10.A strains from complementing to produce a responder F 1 strain. In the case of GLO 9 , histocompatibility restrictions limited antigen presentation. Genetic identity at the I-A subregion was required between the T cells and the APCs but identity at I-E/C was not required. B10.A(5R) responder T cells could be stimulated by GLO 9 -pulsed spleen cells from F 1 progeny of B10 crossed with B10.A, B10.BR, B10.D2, B10.P, and B10.RIII but not B10.Q, B10.M and B10.BSVS. This pattern correlates with the data of others on the serological presence of Ia.7 and the biochemical presence of an I-E/C subregion gene product in these strains. The data suggest that the Ia.7-bearing, I-E/C gene products of the complementing strains are all similar and that this molecule (presumably an Ia α chain) is critically involved in the presentation of GLO 9 . Overall the experiments support the conclusion that both complementing Ir gene products must interact at the molecular level in the same APC in order to generate a T-lymphocyte proliferative response.