Anti-IRF4 Monoclonal antibody, clone 4F5 [PE]

Background and Purpose-Inflammatory mechanisms can exacerbate ischemic tissue damage and worsen clinical outcome in patients with stroke. Both alpha beta and gamma delta T cells are established mediators of tissue damage in stroke, and the role of dendritic cells (DCs) in inducing the early events of T cell activation and differentiation in stroke is not well understood. Methods-In a murine model of experimental stroke, we defined the immune phenotype of infiltrating DC subsets based on flow cytometry of surface markers, the expression of ontogenetic markers, and cytokine levels. We used conditional DC depletion, bone marrow chimeric mice, and IL-23 (interleukin-23) receptor-deficient mice to further explore the functional role of DCs. Results-We show that the ischemic brain was rapidly infiltrated by IRF4(+)/ CD172a(+) conventional type 2 DCs and that conventional type 2 DCs were the most abundant subset in comparison with all other DC subsets. Twenty-four hours after ischemia onset, conventional type 2 DCs became the major source of IL-23, promoting neutrophil infiltration by induction of IL-17 (interleukin-17) in gamma delta T cells. Functionally, the depletion of CD11c(+) cells or the genetic disruption of the IL-23 signaling abrogated both IL-17 production in gamma delta T cells and neutrophil infiltration. Interruption of the IL-23/ IL-17 cascade decreased infarct size and improved neurological outcome after stroke. Conclusions-Our results suggest a central role for interferon regulatory factor 4-positive IL-23-producing conventional DCs in the IL-17-dependent secondary tissue damage in stroke.

B cell and plasma cell fates are controlled by different transcriptional networks, as exemplified by the mutually exclusive expression and cross-antagonism of the B cell identity factor Pax5 and the plasma cell regulator Blimp1. It has been postulated that repression of Pax5 by Blimp1 is essential for plasma cell development. Here, we challenged this hypothesis by analyzing the Igh(Pax5/+) mouse, which expressed a Pax5 minigene from the immunoglobulin heavy-chain locus. Despite high Pax5 expression, plasma cells efficiently developed in young Igh(Pax5/+) mice at steady state and upon immunization, while their number moderately declined in older mice. Although Pax5 significantly deregulated the plasma cell expression program, key plasma cell regulators were normally expressed in Igh(Pax5/+) plasma cells. While IgM and IgA secretion by Igh(Pax5/+) plasma cells was normal, IgG secretion was modestly decreased. Hence, Pax5 repression is not essential for robust plasma cell development and antibody secretion, although it is required for optimal IgG production and accumulation of long-lived plasma cells.