['Circumstantial evidence suggests that Propionibacterium acnes has a role in the inflammation of acne. This could be effected by antigenic or superantigenic or mitogenic reactions.', 'The purpose of this investigation was to determine whether P. acnes had only antigenic activity or additional superantigenic and mitogenic activity.', 'A lymphocyte transformation assay was used to detect responses to a mixture of eight P. acnes whole cell isolates, and their supernatant culture fluids. In order to determine the nature of T-cell reactions to P. acnes cells a mouse-antihuman major histocompatibility complex class II monoclonal antibody was used in the lymphocyte transformation assay to inhibit the antigenic stimulation of lymphocytes. An analysis of the T-cell receptor (TCR) variable region beta (BV) repertoire was undertaken using flow cytometry of the unstimulated and stimulated cells.', 'Peripheral blood mononuclear cells (PBMNC) from adults with no history of acne responded strongly to stationary growth phase cells of P. acnes, less strongly to cells in the exponential growth phase. No response was detected to supernatant culture fluids. PBMNC from five cord blood samples (CBMNC) responded maximally after 3 and 7 days of incubation with stationary growth phase cells of P. acnes. The reaction of CBMNC to P. acnes cells was not suppressed completely by the blocking antibody. The analysis of the TCRBV repertoire indicated that P. acnes induced no deletion or over-representation of certain BV element-bearing T cells. The TCRBV analysis was repeated after preincubation with the blocking antibody. Deletion of T cells bearing certain BV components occurred and there was no over-representation of T cells carrying certain BV components.'] Does propionibacterium acnes and inflammation in acne ; P. acnes have T-cell mitogenic activity?