The Geha laboratory investigates the molecular mechanisms of primary immunodeficiency diseases and atopic dermatitis. It cloned a WASP interacting protein in the yeast two-hybrid system and named it WIP. WIP inhibits WASP function in vitro and binds both G and F actin. WIP KO were made and were shown to have a severe T cell activation defect. WIP shuttles WASP to the immune synapse and is critical for Il-2 responsiveness, WIP functions as a chaperone for WAP. WASP protein, but not mRNA, levels were severely diminished in T cells from WIP-/- mice, and were restored by introduction of WIP. Calpain and proteasome inhibitors restored WASP levels in T cells from WIP-/- mice and from WAS patients with missense mutations that disrupt WIP binding, and corrected the defect in actin polymerization. Current efforts are directed towards constructing mice that expressa small 39 a.a. Wip fragments that restores WASP levels in WWIP KO mice and that disrupts the WASP-WIP interaction in WT T cells. Three other knockouts of genes that are in the WASP WIP pathway have been performed and are being characterized.
The Geha lab has recently conducted a series of studies on the TNF family molecules BAFF and APRIL and showed that they induce isotype switching, particularly to IgA, mostly via TACI, but also via BAFF-R receptors engaged by both APRIL and BAFF. APRIL KO were also generated and were found IgA deficient. Very recently mutation in TACI were found in patients with common variable immunodeficiency (CVID) and IgA deficiency. We are constructing TACI knockin mice to examine the molecular and biochemical effects of human TACI mutations.
LRRC8 is a gene implicated in agammaglobulinemia because a patient with no B cells was found to have a balanced translocation that involves LRRC8 deleting a segment of its extracellular domain. We knocked out LRRC8 Surprisingly the knockout has a severe block in thymic differentiation at the very early double negative stage but normal B cell development indicating that the human mutation is not a dominant negative and suggesting a central role of LRRC8 in thymic development. Further characterization of the Ko is in progress. A knockin that mimics the human mutation is planned.
The Geha lab developed, 7 years ago, a mouse model of atopic dermatitis (AD) elicited by epicutaneous (EC) sensitization with ovalbumin. We have used and continue to use this model to understand the local factors elicited by mechanical skin injury caused by scratching that modulate the strong Th2 and the Th17 response observed following EC sensitization. We are also studying mice deficient in the skin protein fillagrin, which is mutated in 15% of patients with AD.
Dr Geha heads the Animal Consortium of NIH Atopic Dermatitis Vaccinia Network (ADVN), a multicenter study aimed at understanding the basis of the susceptibility of patients with AD to eczema vaccinatum (EV) and vaccinia dissemination. He has 2 projects: one aims to establish an EV model in mice, the other to understand the role of cells cytokines and skin mediators in the EV model.
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