Immune Response to Nocardia brasiliensisAntigens in an Experimental Model of Actinomycetoma in BALB/c Mice

Nine- to twelve-week-old BALB/c mice were injected in footpads with 107 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-g) were determined by
enzyme-linked immunosorbent assay in the sera of infected animals. The circulating levels of IFN-g 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.