Abstract Nocardia brasiliensis is is an intracellular microbe that replicates in host macrophages. We developed an actinomycetoma model in BALB/c mice and showed that IgM but not IgG anti-N. brasiliensis antibodies conferred protection and prevent ed actinomycetoma lesion. The survival or death of the bacterium, once in macrophages, possibly depends on the antibodies used to opsonize N. brasiliensis. We constructed a recombinant strain of N. brasiliensis that produces a green fluorescent protein (GFP) to evaluate virulence and role of IgG and IgM antibodies in cytokine production by macrophages in BALB/c mice. The recombinant N. brasiliensis strain expressing the green fluorescent protein constructed by adding a plasmidic vector containing the GFP gene was used to infect BALB/c mice and macrophages to evaluate phagocytosis and cytokine production with opsonizing IgG and IgM antibodies. N. brasiliensis GFP induces actinomycetoma as well as N. brasiliensis WT. The production of IL-12 with opsonized bacteria increased with IgG and decreased with IgM antibodies. TNF- α production was greater at 24 and 48 hours in non-opsonized bacteria. Opsonized bacteria with IgG and IgM antibodies decreased TNFα production but only IgM isotype antibodies decreased IL-12 production by macrophages. The modified N. brasiliensis strain conserves its property to induce disease.