The present invention relates to a method and composition for inducing lymphocyte proliferation and migration, and for reducing the risks of microbial infections in patients immuno-suppressed. The present invention particularly relates to the use of S100 protein, such as MRP, to induce the proliferation, differentiation and release of immune cells from bone marrow. More particularly, S100A8, S100A9, S100A12 and S100A8/A9 are administered to patients with lowered neutrophil blood concentrations.