The Geha laboratory focuses on the molecular basis and mechanisms of (1) primary immune deficiency diseases and (2) atopic dermatitis.

Genetics and molecular basis of novel primary immunodeficiencies:

Primary immunodeficiencies (PID) are genetic disorders that impair the development and/or function of the immune system. Individuals with PID develop recurrent infections, autoimmune disease, and malignancies; severe immunodeficiencies are fatal without diagnosis and treatment. We use genetic and molecular approaches combined with animal models to define the pathology of immunodeficiency diseases.

Genetic studies:

Identification of the genetic basis of novel PIDs. The advent of whole genome and exome sequencing has facilitated discovery of novel genetic causes underlying PIDs. The Geha lab utilizes functional immunologic assays as well as whole genome/exome sequencing to identify the causative mutation(s) for patients with uncharacterized PIDs. Biochemical and molecular assays as well as mouse models are then used to investigate the pathogenic effect of the mutation and to study gene function in depth. Dr. Geha chairs the International Consortium for Primary Immunodeficiency diseases, an international network of medical and research centers in many countries including Greece, Kuwait, Saudi Arabia, Morocco, UAE, Turkey, Egypt, and Lebanon. This collaboration enables the exchange of expertise in primary immunodeficiency research among all members. These studies are critical not only for the diagnosis of patients with rare PIDs, but also for advancing our understanding of normal immune function. They have resulted in the recent discovery of several new genes that cause PIDS

Molecular studies:

Role of DOCK8 in Innate immunity: The adaptors DOCK8 and MyD88 have been linked to serological memory. DOCK8-deficient patients have impaired antibody responses and considerably fewer CD27+ memory B cells. Recently, we established that DOCK8 functions as an adaptor in a TLR9-MyD88 signaling pathway in B cells. Current ongoing investigations involve the role of DOCK8 in signaling and in immune cell function using DOCK8 knockout mice.

Signaling to the cytoskeleton in lymphocyte function: A dynamic actin cytoskeleton is essential for many cellular functions, including cell adhesion and migration. Lymphocytes of patients with the primary immunodeficiency Wiskott-Aldrich syndrome (WAS) display cytoskeletal abnormalities. Patients with WAS have defects in the gene encoding Wiskott-Aldrich Syndrome protein (WASP). In hematopoietic cells, WASP is critical for the function of the actin cytoskeleton. In resting state, WASP, or its non-hematopoietic cell homolog, N-WASP, are auto-inhibited. Many proteins, including Cdc42, SH3 domain containing proteins, and the PCH family protein, TOCA-1, have been shown to activate WASP/N-WASP. We identified and cloned WIP, the only known inhibitor of WASP/N-WASP to date. WIP is also critical for the stability of WASP. To understand the molecular pathology of WAS, the Geha laboratory applies cellular, biochemical, and molecular techniques to study knockout animal models of WIP, WASP, CIP4 and TOCA-1, all of which interact in a macromolecular complex. We aim to determine how cellular signaling is integrated and transmitted to the cytoskeleton. These studies will help define the molecular aspects of lymphocyte function, particularly, activation, adhesion and migration to areas of infection and inflammation.

Molecular studies on atopic dermatitis and food allergy

Although atopic dermatitis (AD) is a common allergic inflammation of the skin, the molecular basis of this disease is poorly understood. To study the mechanisms of allergic sensitization through the skin, the Geha lab established a mouse model of AD that shares several important immunologic, histological and clinical features with human AD. Using this model, we demonstrated that T cells, eosinophils, neutrophils, dendritic cells, cytokines, transcription factors, chemokines, and leukotrienes all play important roles in the development of AD. We also explore the mechanism by which cutaneous sensitization with food allergens increase the risk of anaphylaxis to ingested antigens. This is a clinically important problem as 40% of children with AD have a coexisting food allergy. Up to 48% of AD patients have mutations in the skin barrier protein filaggrin (FLG) gene. The flaky tail (ft/ft) mice have a mutation in the flg gene, resulting in a novel genetic model of AD that mimics closely the human disease. The Geha lab has demonstrated that ft/ft mice are prone to epicutaneous sensitization with protein antigen. Patients with AD have a dry, itchy skin that provokes scratching, which breaches the skin barrier and allows the entry of antigens, ultimately eliciting an allergic immune response. Analysis of the role of FLG in the development of AD and food allergy after cutaneous antigen contact are ongoing. These studies will provide important insights into the mechanisms of AD and food allergy and will identify novel therapeutic targets for this disease.

The AD research group also investigates the mechanisms of eczema vaccinatum (EV), a complication of smallpox vaccination occurring in patients with AD. The Geha lab has established a model of EV and has demonstrated that the cytokine IL-17 promotes vaccinia virus growth IgE-mediated food allergy is prevalent in patients with atopic dermatitis.Epidemiologic studies suggest that cutaneous exposure to food allergens in infants predisposes to IgE-mediated food allergy, implicating the skin as an important portal of sensitization in the pathogenesis of food allergy. We have developed a novel and powerful and physiologically relevant model of food allergy. WT mice epicutaneously (EC) sensitized by application of ovalbumin (OVA), or peanut allergen, to tape-stripped skin undergo IgE- and mast cell (MC)-dependent anaphylaxis in response to oral antigen challenge. Tape stripping of the skin of WT mice resulted in the expansion of MCs in the jejunum that affected primarily mMCP6+ connective tissue MCs (CTMCs). Current efforts are directed at understanding the role of CTMCs in food anaphylaxis and the crosstalk between skin and gut.