A SUBUNIT 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 pes tis by injection of an alhydrogel-adsorbed bed sub-unit vaccine has be en compared with that given by an existing killed whole cell vaccine l icensed for human use, The sub-unit vaccine protected mice against exp osure to > 10(4) colony-forming units (c.f.u.) of virulent plague orga nisms (100 LD50 doses), whereas tile 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 signif icant levels of Ige to Fl only were detectable inequivalent samples. L evels of F1-specific Ige in serum, secreted from spleen cells and in B AL were significantly higher (P < 0.01) in sub-unit compared with kill ed whole cell vaccinees. IgA was not detected in BAL from intra-muscul arly nosed sub-unit vaccinees and thus the protection achieved against inhalational challenge with Yersinia pestis is attributed to the indu ction of systemic immunity to both the F1 and V antigens in the sub-un it 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.