The effect of CD21 on proliferation and differentiation on human cervical epithelium
CD21 is a transmembrane receptor molecule, previously known as the CR2, C3d or EBV receptor, which was originally identified and characterized on the B-cell lymphoid series. It has also been described in various squamous cells but these reports are diverse and sometimes conflicting. This thesis is a study of putative CD21 on the squamous cells of the human cervix uteri. The introduction provides background information on the cervix and on CD21 and indicates lines of investigation followed later. Experimental studies commence with an immunohistochemical study in which a panel of anti-CD21 monoclonal antibodies was applied to fresh frozen sections of the cervix. Only one antibody, HB5 reacted positively and this was consistent. HB5 located to the cell membrane of normal squamous ectocervical cells in a band-like manner, above the basal layers and beneath the superficial layers. Significantly HB5 did not react with CIN or koilocytes. That only HB5 reacted was subsequently confirmed by flow cytometry. That it reacted only with cell membrane was confirmed by confocal laser microscopy. Further, the lower limit of the HB5 positive band was confirmed by a dual labeling study employing HB5 and MIB-1 which recognizes cycling cells. Cells labeled with these antibodies appear mutually exclusive. Cycling cells in vivo are not HB5 positive. Western blotting studies on extracts of normal cervical epithelium indicated that HB5 reacted with a molecule larger than that found on lymphoid cells. However, they do share the same epitope. Having demonstrated an HB5 epitope on epithelial cells which were not cycling but were not yet fully differentiated, a series of in vitro experiments were conducted to see if the epitope was functional in a receptor sense, or was an epiphenomenon. Monolayer cultures, with appropriate controls, were exposed to HB5. Small effects were demonstrated in thymidine incorporation, protein synthesis and cell numbers, in early culture stages. The concluding general discussion gives some thought to the possible role of maturation in the control of neoplasia.