G. Bikah et al., A ROLE FOR CD5 IN COGNATE INTERACTIONS BETWEEN T-CELLS AND B-CELLS, AND IDENTIFICATION OF A NOVEL LIGAND FOR CD5, International immunology (Print), 10(8), 1998, pp. 1185-1196
CD5 is a glycoprotein expressed at a high level on the surface of matu
re T lymphocytes. Studies with CD5 mAb and CD5-deficient mice have sho
wn that the CD5 molecules have a significant role in T cell growth res
ponse. However, the precise role of CD5 in immune cell interactions is
still unclear. The present study provides evidence that CD5 plays a d
irect role in providing growth signals during the contact-dependent ac
tivation and proliferation of splenic a cells. An anti-CDS mAb inhibit
ed T(h)1- and T(h)2-type cell-induced a cell proliferation. CD5-Ig, a
chimeric fusion protein, induced proliferation of resting a cells. Flo
w cytometric analyses using CD5-Ig and mAb to CD72 demonstrated that C
D5 bound to a ligand (CD5L), and this binding was not blocked by a var
iety of anti-CD72 mAb, Also, CD5-Ig did not bind to CD72(+)-transfecte
d cells. Immunoprecipitation of surface labeled a cell molecules with
CD5-Ig showed that CD5L was composed of 77-80 and 38-40 kDa polypeptid
e chains, distinct from CD72, CD5L was expressed on activated splenic
a cells, but not T cells, whereas its expression was constitutive on p
eritoneal a cells and on a lymphoma cell lines.