Cyclosporin is an immunosuppressant that acts by selectively inhibitin
g the activation of T lymphocytes. Its effects on monocytes and neutro
phils are not well explored. We investigated the in vitro effects of c
yclosporin on these cells, harvested from venous blood from nine healt
hy, nora-smoking volunteers. In vitro incubation of monocytes with inc
reasing concentrations of cyclosporin (5, 25 and 625 mu g) depressed t
heir phagocytosis by 22%, 32% and 49%, respectively, compared to the c
ontrol values. The intracellular killing capacity of monocytes decreas
ed by 26%, 31% and 43% with these doses, and neutrophil phagocytosis w
as depressed in a similar manner (16%, 30% and 40%). Patients receivin
g cyclosporin are susceptible to infections, and inhibition of these p
hagocytic cells by cyclosporin may be partly responsible for this. Neu
trophil chemotaxis is reduced in patients with impaired renal function
. Treating these patients with cyclosporin may in addition suppress th
e phagocytic function of these cells.