Bacteria of human physiological microflora liberate immunomodulating peptides.

Human isolates of Propionibacterium acnes and Staphylococcus saprophyticus could be shown to liberate low molecular weight peptides (MW less than 6.500 D) with immunomodulating activity. FACS analyses of BALB/c-mouse lymphoid cells from the thymus and spleen revealed an enhanced percentage of T-helper cells after peptide administration. Intestinal microflora decontamination of BALB/c-mice considerably reduced immune cell function and lymphatic tissue proliferation. Apparently, lack of peptide production or liberation correlated to immunosuppression. Substitution of peptides (from P. acnes or S. saprophyticus) to decontaminated mice reconstituted immune cell function and proliferation. Cortisone-resistant thymocytes were used as an experimental equivalent of functional cells in the thymus. Thus, cortisone treatment of BALB/c-mice significantly reduced the number of thymocytes, however, administration of microbial peptides restored the thymus population.