LUNG-PHASE RESISTANCE AGAINST CHALLENGED SCHISTOSOMA MANSON! INFECTION IN MICE IMMUNIZED WITH SOLUBLE EGG ANTIGEN
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A histological and immunohistochemical study was made on schistosomula, associated inflammatory reactions and deposition of schistosomal antigens in lung tissues of normal mice and mice immunized will; partially purified soluble egg antigen (SEA) of molecular weight 100-137k dalions. Schistosomula and inflammatory foci were counted by histologic scoring in 20 lung sections/mouse taken at intervals of 30 p apart. Results showed that in normal mice, schistosomula number reached their peak on day 7 post infection then rapidly decreased until they were barely detectable on day 25. In immunized mice, they reached their peak on day 9 then gradually decreased so as many worms were still retained in the lungs on day 25. Mat is, the rate of elimination of lung schistosomula was much slower in immunized mice. The pulmonary cellular reaction in immunized mice was evident as early as day 7 and from day 9 onwords, mononuclear infiltrations were increasing. Inflammatory foci appeared earlier (day 7) and significantly increased on subsequent days. The reaction, therefore, was anamnestic, most probably of delayed type hypersensitivity (DM) response. In normal mice, the reaction was mild and started late. Schistosomal antigen deposition in lung tissues was markedly augmented in immunized mice with inure consequent stimulation of the immune response. So, this study indicates that immunization with this type of antigen causes augmentative lung resistance against challenge infection as it was effective in blocking migration of schistosomula by stimulating inflammation in lung tissues and so may be of value in vaccination studies against schisto.s'omiasis. However, it should be necessary to guard against excessive inflammation and pulmonary fibrosis.