Funktionelle Analyse von MHC-Klasse-I-Genen der Rhesusaffen (<i>Macaca mulatta</i>)

Abstract

This thesis focuses on the structure and function of rhesus macaque (Macaca mulatta, Mamu) major histocompatibility complex (MHC) class I genes. As the cellular immune response is at least partly controlled by MHC class I molecules new insights in the structure and function of this group of molecules will advance our understanding of the rhesus monkey s immune response and how results of infectious studies in macaques can be transferred to the human system. The human MHC class I molecules (HLA-A, -B and -C) are characterized by a high degree of polymorphisms. A complete sequenced haplotyp of the rhesus macaque MHC revealed considerable differences compared to humans with regard to extensive duplications and haplotypic presence-absence polymorphisms. The functional significance of this plethora of MHC class I genes remains, however, unknown so far. One goal of this study was the characterization of Mamu-A and Mamu-B genes by means of expression studies as well as the functional analysis. Therefore five Mamu-A, 13 Mamu-B, one Mamu-I and one Mamu-E stable transfectants were established. Furthermore, confocal microscopy and flow cytometry studies revealed high levels of MHC class I surface expression for Mamu-A molecules. On the other hand Mamu-B molecules exhibited divergent expression patterns, including surface and intracellular expression for some alleles. These results indicate a heterogeneous system of MHC class I function in rhesus macaques. Immunological assays for natural killer (NK) cell cytocoxity and for NK cell activation (via degranulation) identified Mamu-A molecules as a target site for inhibitory NK cell receptors leading to an inhibitory effect on NK cell activation. Additionally, molecules encoded by the Mamu-A1 gene have been shown to be more potent in inhibition of NK cell activation than the molecules encoded by other Mamu-A genes. Human MHC class I molecules are ligands for killer cell immunoglobulin-like receptors (KIR) on NK cells. In this study specific interactions between Mamu-A and KIR molecules were shown in an in vitro model system. The presented results give rise to the assumption of MHC-A molecules in rhesus macaques playing a central role in NK cell regulation, whereas in higher primates (e. g. human and chimpanzee) MHC-C contribute as the major ligand for NK cell receptors.