E protein function in activated B cell subsets

Mature B lymphocytes are capable of acquiring adaptive immune function based upon several selective and diversification processes, which allow potent antibody responses. It is speculated that E proteins play an important role in such events, as they are a class of basic helix-loop-helix transcription factors involved in a multitude of hematopoetic developmental pathways. While the function of E proteins in early B lymphopoiesis is well characterized, less is known about these DNA binding factors in the later stages of B cell maturation. Here, using a combination of in vivo and in vitro methods, we studied the germinal center reaction, class switch recombination, and plasma cell development in mice lacking the E proteins E2A and HEB in an attempt to better understand the participation of E2A and HEB in antigen- activated B cell formation. In vivo, lethally irradiated mice transplanted with E2A and HEB null bone marrow are deficient in class switch recombination and subsequent plasma cell function. In vitro experiments show that the E proteins E2A and HEB are both required for efficient humoral immunity. Mice lacking one or both of these E proteins demonstrate perturbed isotype switching and plasma cell differentiation in activated B cell cultures. We further identify impaired expression of genes involved in the germinal center reaction and plasma cell development. Taken together, these data suggest that E2A and HEB function in the germinal center by controlling two mutually exclusive transcriptional programs that ultimately drive B cell activation. We additionally examined genome-wide H3K3 monomethylation patterns in naïve and germinal center B cells. This analysis has confirmed the importance of E2A in late and end stage B cell development and ultimately suggests differences in the enhancer repertoire of naïve B lymphocytes in comparison to antigen-dependent B cell lineages