Effects of anti-CD18 and LPS on CD14 expression on human monocytes

In this study we show that the cytokine stimulatory effect of LPS on human monocytes is enhanced by addition of monoclonal antibodies against CD18 (alpha CD18 MoAbs). Incubation of monocytes with alpha CD18 MoAbs overnight increased the CD14 expression as detected by Leu-M3, but not with My-4. These results indicate that CD18 participates in LPS-induced TNF-alpha production as well as in regulating CD14 expression on monocytes. Addition of LPS to monocytes resulted in a reduction in the CD14 expression after 1/2, 1, 2 and 4 h, but increased CD14 expression was seen after LPS stimulation overnight. By doing double labelling of the monocyte population for CD14 and CD16 it was found that the reduction in CD14 expression occurred in the CD14+/CD16+ sub-population, while the increase in CD14 expression was seen in both the CD14+/CD16- and the CD14+/CD16+ cells. alpha CD14 MoAbs that were able to inhibit LPS-induced cytokine production from monocytes (3C10 and My-4) were considerably less able to detect the increase in CD14 expression after LPS stimulation than alpha CD14 MoAbs that did not inhibit LPS-induced cytokine production (Leu-M3 and alpha CD14Serva). Our data indicate that My-4 and Leu-M3 define two populations of CD14+ cells on LPS stimulated human monocytes.