Treatment with Propionibacterium acnes modulates the late phase reaction of immediate hypersensitivity in mice

The administration of killed Propionibacterium acnes suspension to mice enhances macrophage phagocytic and tumoricidal activities, have an adjuvant effect to antibody response and increases resistance to infection. Recent reports demonstrated that P. acnes treatment promotes IL-12 and IL-18 synthesis in mice inducing IFN-gamma release, enhancement of IgG2a switch and inhibition of Th2 cell expansion. These findings led us to investigate whether P. acnes could modulate hypersensitivity type I reaction observed in a murine model. Animals were implanted with heat coagulated hen's egg white (HEW) into the subcutaneous tissue, followed by OVA-challenge in the footpad. The observed reaction was characterized by elevated Th2 cytokine levels, especially IL-4 and increase in eosinophil infiltration as occurs in the late phase reaction (LPR) of type I hypersensitivity, a pattern observed in allergic asthma in human. Two different biological effects were induced by killed P. acnes depending on the experimental protocol used. When mice were treated with one dose of P. acnes per week during 3 weeks and the last dose administrated at the same time of HEW implantation, a strong adjuvant effect on type I hypersensitivity reaction with intense eosinophilic infiltration was observed. On the other hand, when the HEW implant was made 1 week after the administration of the last dose of P. acnes, animals developed a typical delayed type hypersensitivity reaction, and a cytokines pattern characteristic of the Th1 immune response.