The suppressive effect of serum samples from patients with chancroid on human mononuclear cells correlates with the clinical picture and is interleukin-2-dependent.

Plasma samples from patients with chancroid diagnosed both on clinical and microbiological grounds were assessed for their ability to inhibit mitogen-induced proliferation of human lymphocytes from healthy donors. All serum samples analysed suppressed phytohaemagglutinin A (PHA) blastogenic response. A significant difference in the observed extent was seen when serum samples from patients with and without associated lymphadenopathy were compared (P < 0.05). Using an interleukin-2 (IL-2)-dependent cell line it could be demonstrated that the addition of patients' plasma to cultured cells markedly depressed mitogen-induced IL-2 synthesis. Results presented suggest that cell-mediated mechanisms play a role in the pathogenesis of infection due to Haemophilus ducreyi.