Supplementary MaterialsSupplemental. serve to promote long-lived humoral immune responses (Crotty, 2011). In contrast to other T effector (Teff) cells that egress from your secondary lymphoid organs (SLOs) DSM265 following activation by dendritic cells, Tfh cells occupy a specialized niche within the SLOs by migrating deep into the B cell follicle. Within this niche, cognate interactions with antigen-presenting B cells drives the germinal center (GC) reaction and this response must be maintained to generate affinity matured memory B cells and plasma cells (Liu et al., 2015; Shulman et al., 2014). Even though Tfh effector program is critical for antibody-mediated protection against extracellular pathogens, uncontrolled Tfh cell responses can lead to immunopathology and autoimmune disease (Tangye et al., 2013). Thus it is essential to understand the regulatory mechanisms involved in Tfh cell differentiation as well as maintenance to promote health and prevent disease. The transcription factor B cell lymphoma (Bcl)-6 is usually indispensable for Tfh cell differentiation and represses important signaling pathways that drive alternative CD4+ effector cell fates (Hatzi et al., 2015; Johnston et al., 2009; Nurieva et al., 2009; Yu et al., 2009). In contrast to other effector subsets in which cytokine signaling drives expression of lineage-specific transcription factors required for their differentiation, specific cytokines that selectively polarize Tfh cells have not been recognized. By contrast, proteins associated with co-stimulation or intercellular adhesion such as CD28 and ICOS promote the initiation and persistence of Tfh cells (Choi et al., 2011; Linterman et al., 2014; Linterman et al., 2009). However, whether CD28 and ICOS signaling directly regulate Bcl-6 expression is not obvious. In addition, SLAM family members are critical for sustained T-B cell interactions and GC formation, but are not required for DUSP1 initiation of Tfh cell differentiation (Cannons et al., 2010; Qi et al., 2008). DSM265 Thus, factors that promote Tfh cell lineage specification remain to be decided. Integrins are heterodimeric receptors expressed by leukocytes and play essential functions in leukocyte migration, tissue retention and immunological synapse formation (Evans et al., 2009). One member of the integrin family, leukocyte function-associated antigen (LFA)-1, is composed of the L and 2 subunits and has been shown to be a potent intercellular adhesion and co-stimulatory molecule for T DSM265 cell activation in vitro (Dubey et al., 1995; Dustin and Springer, 1989). These findings have been substantiated by in vivo studies in which deficiency in either subunit compromises T cell priming and is associated with decreased antigen-specific antibody production in humans and mice (Fischer et al., 1986; Kandula and Abraham, 2004; Morrison et al., 2015; Peters et al., 2012). Importantly, LFA-1 activity is not only regulated by its expression but also by its conformation around the cell surface. Indeed, conversion to an open conformation by T cell receptor (TCR) or chemokine-mediated signaling increases the binding affinity for numerous LFA-1 ligands of the intercellular adhesion molecule (ICAM) family (Hogg et al., 2011). However, the in vivo role of DSM265 integrin activity in CD4+ T cell lineage commitment, in general, and Tfh cell biology specifically, has not been examined. Given the unique differentiation requirements of Tfh cells, we hypothesized that integrins play an important role in elaborating the Tfh effector cell program. Here we demonstrate that Tfh cells expressed a highly active form of LFA-1 that promoted maintenance of this effector subset within the GC niche. In addition, we found that LFA-1 activation enhanced CD4+ T cell expression of Bcl-6 in the context of TCR triggering. Inhibition of LFA-1 signaling compromised Tfh cell differentiation and prevented the generation of protective humoral immunity to intestinal helminth contamination. Finally, we showed that deletion of Talin-1, an adaptor protein critical for generating the high-affinity conformation of LFA-1, selectively compromised Bcl-6 expression and Tfh cell development during contamination. Our results reveal previously undefined functions for the integrin LFA-1 in controlling the initiation and persistence of Tfh cells and suggests an important target for controlling T-dependent humoral immune responses. RESULTS Tfh Cells Exhibit Elevated Expression of the Integrin LFA-1 We have previously shown that Tfh cells are the dominant.