A sub-unit vaccine elicits IgG in serum, spleen cell cultures and bronchial washings and protects immunized animals against pneumonic plague

In this study the protection afforded against aerosolized Yersinia pestis by injection of an alhydrogel-adsorbed bed sub-unit vaccine has been compared with that given by an existing killed whole cell vaccine licensed for human use, The sub-unit vaccine protected mice against exposure to > 10(4) colony-forming units (c.f.u.) of virulent plague organisms (100 LD50 doses), whereas the whole cell vaccine provided only 50% protection against 1.8 x 10(3) c.f.u. In subunit vaccinees, IgG to each of the F1 and y antigens contained in the vaccine, was detected in serum, on direct secretion by spleen cells and in broncho-alveolar washings (BAL). In killed whole cell vaccinees, physiologically significant levels of Ige to Fl only were detectable inequivalent samples. Levels of F1-specific Ige in serum, secreted from spleen cells and in BAL were significantly higher (P < 0.01) in sub-unit compared with killed whole cell vaccinees. IgA was not detected in BAL from intra-muscularly nosed sub-unit vaccinees and thus the protection achieved against inhalational challenge with Yersinia pestis is attributed to the induction of systemic immunity to both the F1 and V antigens in the sub-unit vaccine, The enhanced protective efficacy of this sub-unit vaccine over an existing vaccine has been demonstrated in all animal model of pneumonic plague. (C) 1997 Elsevier Science Ltd.