FITC
Excitation: 490nm, Emission: 525nm
The CD53 pan-leukocyte glycoprotein is a member of the recently described tetraspan family of cell membrane proteins. The structure and functional characteristics of these molecules indicate that they may play important roles in transmembrane signaling in different cells. Recently, it was reported that cross-linking of CD53 on human B cells led to an increase in cytoplasmic calcium fluxes. In the present study, we wished to further explore the possible role of CD53 in functional B cell responses. Cross-linking of CD53 with the use of the mAb MEM-53 and a polyclonal sheep anti-mouse Ig promoted activation of resting B cells into the G1 phase of the cell cycle as judged by increased expression of the early activation Ag CD69, increases in cellular volume, RNA synthesis, and c-myc protein levels, and enhanced binding of 7-aminoactinomycin D. In contrast, MEM-53 alone had no detectable effects. Cross-linking of anti-CD53 induced negligible S phase entry in the absence of other stimuli. However, cytokines, in particular IL-2 and IL-4, potentiated the DNA synthesis induced by cross-linking of CD53. Furthermore, cross-linking of the CD53 Ag induced Ig production in the presence of T cell supernatant. Taken together, the data suggest that CD53 plays an important functional role in B cell activation and differentiation.
Monoclonal antibodies against several human leucocyte cell surface antigens were prepared and characterized: (1) MEM-56, MEM-93, MEM-66, and MEM-104 against the CD45R antigen (220 kDa and 205 kDa mol. wt. forms of the leucocyte common antigen CD45 expressed on B-lymphocytes, myeloid cells and a subpopulation of T-lymphocytes); (2) MEM-98 and MEM-100 against the T-lymphocyte antigen CD6 (mol. wt. 100 kDa); (3) MEM-85 against the broadly expressed antigen CD44 (mol. wt. 85 kDa) which was recently shown by us to be identical with the lymphocyte homing receptor; (4) MEM-53 against a newly described broadly expressed antigen of 35-40 kDa mol. wt. and (5) MEM-102 against another newly described glycoprotein of 40 kDa mol. wt. anchored in membrane through a phosphatidylinositol moiety.
