Localization of intracellular monoclonal antibody specific for mycobacteria in experimentally induced pulmonary tuberculous lesion

To determine the intracellular localization of intravenously injected infection specific monoclonal antibodies (mAbs) in the infected cells, immunohistochemical staining was carried out in an animal model having pulmonary tuberculous lesions induced by inoculation of heat-killed Mycobacterium tuberculosis H₃₇RV. One milligram of intact mouse mAb against mycobacteria (group 1, n=10) and F(ab')₂ (group II, n=6) was intravenously injected to the rabbits of each group. Immunohistochemical staining using an antimouse Ab was performed at days 1, 3, 5, 7 and 8 in group I and at days 1, 2 and 3 in group II by the streptavidin-biotin method. For the control study 1 ml of nonspecific polyclonal human IgG (group III, n=10) and 100 (.ig of normal rabbit IgG F(ab')₂ (group IV, n=6) was injected to rabbits and guinea pigs having tuberculous inflammation, respectively. Both groups (groups I and II) showed a positive antigen (Ag)-Ab reaction within the cytoplasm of monocytes. A weak but positive reaction was observed intracellularly in group III; however, no positive reaction was seen in group IV Our results suggest that an intracellular Ag-Ab reaction plays an important role in the localization of infection by immunoscintigraphy using specific mAb fragments.