Activating and inhibitory functions for the histone lysine methyltransferase G9a in T helper cell differentiation and function

Blimp1: driving terminal differentiation to a T

B lymphocyte maturation-induced protein-1 (Blimp1) is a transcriptional repressor expressed in diverse cell types. In the adaptive immune system, Blimp1 is expressed in lymphocytes that have undergone effector differentiation. Blimp1 is a master regulator of plasma cell differentiation and plays important roles in controlling T cell homeostasis and effector differentiation. Blimp1 can be induced by a variety of cytokines including IL-2, IL-4, IL-12, and IL-21 in addition to TCR and co-stimulatory signals. Blimp1-deficient mice develop spontaneous inflammatory disease mediated by infiltration of activated T cells into tissues. During immune responses Blimp1 is required for the differentiation of plasma cells as well as short-lived CD8(+) cytotoxic T cells. Mounting evidence suggests that Blimp1 plays a common role in the terminal differentiation of multiple cell subsets.

Self/nonself perception, reproduction and the extended MHC

Self/nonself perception governs mate selection in most eukaryotic species. It relies on a number of natural barriers that act before, during and after copulation. These hurdles prevent a costly investment into an embryo with potentially suboptimal genetic and immunological properties and aim at discouraging fertilization when male and female gametes exhibit extensive sharing of alleles. Due to the fact that several genes belonging to the extended major histocompatibility complex (xMHC) carry out crucial immune functions and are the most polymorphic within vertebrate genomes, it is likely that securing heterozygosity and the selection of rare alleles within this gene complex contributes to endowing the offspring with an advantage in fighting infections. Apart from MHC class I and II antigens, the products of several other genes within the xMHC are candidates for participating in mate choice, especially since the respective loci are subject to long-range linkage disequilibrium which may aid to preserve functionally connected alleles within a given haplotype. Among these loci are polymorphic odorant receptor genes that are expressed not only in the olfactory epithelium, but also within male reproductive tissues. They may thus not only be of importance in olfaction-influenced mate choice, by recognizing MHC-dependent individual-specific olfactory signals, but could also guide spermatozoa along chemical gradients to their target, the oocyte. By focusing on the human HLA complex and genes within its vicinity, we show here that the products of several xMHC-specified molecules might be involved in self/nonself perception during reproduction. Although the molecular details are often unknown, the existence of highly diverse, yet intertwined pre- and post-copulatory barriers suggests that xMHC-encoded proteins may be important for various stages of mate choice, germ cell development, as well as embryonic and foetal life in mammals and other vertebrates. Many of these genes should thus be regarded as crucial not only within the immune system, but also in reproduction.