Expression of CD10 by human T cells that undergo apoptosis both in vitro and in vivo

We are glad to hear that Drs Bladon and Taylor1confirmed our data that CD10 can be found on the surface of T cells induced into apoptosis, although they used a somewhat different system. As for the differences reported by Drs Bladon and Taylor, we wish to point out that there are several variables to be taken into account. First, the anti-CD10 mAb employed may greatly influence the results obtained, and the definition of “weak” or “strong” staining varies depending upon the CD10 mAb used. In addition, we believe that staining cannot be defined as percentage of weakly or strongly stained cells because we have better methods of determining immunofluorescence intensity, such as flow-cytometry profiles, as we reported.2 With flow cytometry analyses of peripheral blood from HIV-seropositive individuals, it is possible to segregate populations of CD10⁺/CD3⁺ T cells with various degrees of CD10 positivity that probably represent cells as different stages of the apoptotic process. These CD10⁺ T cells are not necrotic, as demonstrated by triple-staining tests capable of detecting necrotic cells. Perhaps in connection with this, we should mention some of our recent data that show down-regulation of CD10 by necrotic cells.

Second, the methods used to induce apoptosis both in vivo or in vitro may influence the mode and quantity of CD10 expression. This possibility may partly explain some of the differences between the Bladon and Taylor's data and ours. We have evidence in favor of this hypothesis in preliminary studies in which T cells have been induced into apoptosis by different signals or by the same signal with different intensity (ie, different concentrations of CD95 mAb).

We believe that CD10 may have a role in apoptosis, as suggested by the finding that there is considerable CD10 synthesis upon the induction of apoptosis. But it is difficult to accept that the only role of molecules newly synthesized during apoptosis is that of facilitating the clearance of apoptotic cells from circulation. Apoptosis of T (and also B) cells primarily takes place in the peripheral lymphoid organs. The environment is likely to participate in the regulation of apoptosis. Therefore, it is possible that the newly synthesized molecules may play a role in this regulatory process. These considerations may open up new avenues of research on T-cell physiology besides offering the opportunity of discovering new markers which facilitate the in vivo identifications of apoptotic T cells.