Immune response to Nocardia brasiliensis antigens in an experimental model of actinomycetoma in BALB/c mice.

Nine- to twelve-week-old BALB/c mice were injected in footpads with 10(7) CFU of a Nocardia brasiliensis cell suspension. Typical actinomycetoma lesions, characterized by severe local inflammation with abscess and fistula formation, were fully established by day 28 after infection. These changes presented for 90 days, and then tissue repair with scar formation slowly appeared, with complete healing after 150 days of infection. Some animals developed bone destruction in the affected area. Histopathology showed an intense inflammatory response, with polymorphonuclear cells and hyaloid material around the colonies of the bacteria, some of which were discharged from draining abscesses. Sera from experimental animals were analyzed by Western blotting, and immunodominant antigens P61 and P24 were found as major targets for antibody response. Anti-P24 immunoglobulin M (IgM) isotype antibodies were present as early as 7 days, IgG peaking 45 days after infection. Lymphocyte proliferation with spleen and popliteal lymph node cells demonstrated thymidine incorporation at 7 days after infection, the stimulation index decreasing by day 60. Levels of interleukin-1 (IL-1), IL-2, IL-4, IL-6, tumor necrosis factor alpha, and gamma interferon (IFN-gamma) were determined by enzyme-linked immunosorbent assay in the sera of infected animals. The circulating levels of IFN-gamma increased more than 10 times the basal levels; levels of IL-4, IL-6 and IL-10 also increased during the first 4 days of infection.