It has been demonstrated that Brucella abortus is capable to multiply into professional antigen presenting cells such as macrophages and dendritic cells. However, there are a few reports about Brucella infection into B cells. In this work, we evaluated the ability of B. abortus 2308 for infect the human B cell line, NALM6 R. B cells cultured in RPMI medium supplied with L-glutamine and 10% of fetal calf serum were infected with several MOIs of Brucella abortus 2308 transformed by electroporation with the pBBR1MCS-2-gfp-mut3 plasmid to evaluate the entry of green fluorescent Brucella. The percentage of cells containing bacteria was evaluated by flow cytometry at three time points. To evaluate whether Brucella was on the surface or into the B cells, kinetics of infection was performed and analyzed by transmission electron microscopy. Association of Brucella abortus 2308-gfp-mut3 with NALM6 R cells increased in a dose-time dependent manner to reach a maximum of 50% of NALM6 R infected cells. Electronic microscopy revealed that NALM 6R B cells produce filopodia over B. abortus. Once inside, the bacteria resided into small vesicles. Apparently bacteria underwent some bactericidal mechanism, because the electron microscopy showed bacteria degraded into vesicles. It was not observed evidence of replication of bacteria inside B cells. Brucella abortus 2308 is capable to interact with NALM6 R membrane, to induce filopodia formation and to entry into B cells inside vesicles.

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