Isabella Cascino, Giuliana Papoff, Adriana Eramo, and Giovina Ruberti

Department of Immunobiology, Institute of Cell Biology, National Research Council, Rome, Italy.

Received 12/01/95; Accepted 01/11/96; On-line 1/1/96

We are very grateful to R. Tosi and R. Butler for the stimulating discussion and critical reading of the manuscript. This work was partially supported by grant n. 8206-12 AIDS, from National Institute of Health, by a grant from Associazione Italiana per la Ricerca sul Cancro and by the EEC Human Capital and Mobility Program grant CHRX-CT94-0537.