INTERLEUKIN-3 ADMINISTRATION ENHANCES HUMAN MONOCYTE FUNCTION IN-VIVO

In addition to its haemopoietic effects, interleukin-3 (IL-3) enhances leucocyte function in vitro. In this study we examined the effects on haematological variables and monocyte function of a single IL-3 infus ion in five haematologically normal individuals. There was a rapid fal l in circulating monocyte (to 24 +/- 6% of pre-infusion value) and eos inophil numbers (to 3 +/- 2%) with a nadir at 30 min and gradual retur n to baseline over 6 h. No significant changes in monocyte expression of the adhesion molecules CD11b or L-selectin or of monocyte respirato ry burst activity were detected. There was a significant increase in m onocyte phagocytosis and killing of Candida after IL-3 infusion: the p ercentage of monocytes which had ingested Candida increased from 39 +/ - 10% to 62 +/- 12% and the total number of Candida killed per 100 mon ocytes increased from 63 +/- 34 to 210 +/- 59 (P < 0.05 and P < 0.01 r espectively). There was no inhibition of neutrophil migration into a ' skin window' site and monocyte migration was moderately enhanced (peak increase of 260 +/- 47%). These results show that IL-3 has significan t effects on monocyte function in vivo and could be of use in augmenti ng host defence mechanisms in immunocompromised patients.