טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentEiza Nasren
SubjectCD72: Looking for a Potential Regulatory Ligand Soluble
CD72: Immunological Functions
DepartmentDepartment of Medicine
Supervisor Clinical Professor Zahava Vadasz


Abstract

CD72, a 45 kDa type II transmembrane glycoprotein, is a B cell co-receptor, which negatively regulates B cell receptor (BCR) signaling and has a major role in the development of lupus-like autoimmune disease in animal models. Moreover, CD72 has a secreted soluble form (sCD72), highly present in the serum of Systemic Lupus Erythematosus (SLE) patients compared to healthy individuals, positively correlated with disease severity and kidney damage. Semaphorin 3A (Sema3A) is characterized as an immune semaphorin that suppresses the activity of B and T cells and active in the modulation of inflammatory conditions in immune-mediated diseases like SLE. Our group has observed that Sema3A can reconstruct the B cell regulatory function by up-regulating CD72 expression. In this respect, we raise the hypothesis that Sema3A might be a ligand for CD72, with regulatory properties, and sCD72 may have a biological function, probably as an excitatory molecule, that elicits effects on B and/or T cells.

This study presents evidence indicating that Sema3A is an actual ligand for CD72, without requiring the presence of the known Sema3A receptor neuropilin-1 (Nrp1). Sema3A-CD72 signaling inhibits the phosphorylation of STAT-4 and HDAC-1 and induces p38 MAPK and PKC theta phosphorylation in primary B cell-derived B-lymphoblastoid cells (BLCL) lacking Nrp1 expression as well as in primary human B cells from healthy donors and SLE patients. Regarding sCD72, the results show that it does not affect primary human B cells, in contrast to its activation effect on T cells. The addition of sCD72 to cultured T cells induces their proliferation in a dose-dependent manner, increases the CD69 expression, one of the critical activation markers, and increases the expression of the pro-inflammatory cytokines, INF-γ and IL-17A. Furthermore, Mass spectrometry analysis revealed that CD5 and/or CD6 are probably candidates for sCD72 receptor on T cells. Further evaluation of these interactions should be done, especially the contribution of these molecules to SLE pathogenesis. Also, more studies should be done to understand the mechanism responsible for the possible cleavage of the CD72 receptor into a soluble form, mainly in SLE.

To conclude, Sema3A is a functional regulatory ligand of CD72 on B cells, binding CD72 induces signal transduction pathways, inhibits the phosphorylation of STAT-4 and HDAC-1, and induces p38 MAPK and PKC theta phosphorylation, resulting in overproduction of anti-inflammatory and decreases pro-inflammatory cytokines. In contrast, it's secreted form (sCD72) acts as an activating molecule of T cells, resulting in supporting autoimmune diseases. Thus, Sema3A is a promising therapeutic agent as a suppressor of autoimmune diseases, and due to the sCD72 activation effect, prevention of the unknown yet cleavage mechanism may help regulates the immune responses in autoimmune diseases toward rebalancing the immune system.