Apoptosis induced by crosslinking of CD4 on activated human B cells.

Using immunofluorescence, RT-PCR, and Western blotting, we have demonstrated the ability of human B cells to express CD4. In each of the 10 lymphoblastoid cell lines (LCL) tested there was variable, but definite, proportion of CD4-positive B cells. Expression of CD4 was related to the cell cycle; CD4 was expressed in the G1 phase and continued at later phases of the cell cycle.

Promotion and inhibition of haemopoiesis by NK cells: a model for immune-mediated haemopoietic suppression.

Human NK cells, besides mediating cytotoxic functions, can exert a number of regulatory activities on the proliferation and maturation of hematopoietic stem cells through the release of soluble factors. A preliminary characterization of these factors demonstrates that NK cell-derived colony stimulating activities (CSA) are represented by GM-CSF and IL3, whereas the colony inhibiting activity (CIA) produced by NK cells is identifiable as TNF. CSA is mainly released by resting NK cells, while, following appropriate activation, the latter cells produce large amounts of CIA.