To investigate the significance of intercellular adhesion molecule-1 (ICAM-1) and leukocyte function-associated antigen-1 (LFA-1) in host defense against infection with intracellular parasites, we examined the effects of in vivo pretreatment with mAbs to ICAM-1 (1A29) and LFA-1 alpha (WT-1) on the protection against infection with Listeria monocytogenes in Fisher F344/N rats. Expression of ICAM-1 and LFA-1 alpha molecules on T cells in spleen, liver and peritoneal cavity of rats was down-regulated after i.p. administration with daily doses of 300 micrograms of either 1A29 or WT-1 for 10 days. The survival rate of rats inoculated with viable Listeria was significantly reduced by in vivo pretreatment with 1A29 together with WT-1 for 10 days but not by in vivo pretreatment with control mAb. The numbers of bacteria in the spleen in rats pretreated with both 1A29 and WT-1 were significantly increased on day 3 and day 6 after infection with 1 x 10(7) of viable Listeria corresponding to 1/30 of LD50 to normal rats. Thus, the resistance against listerial infection was severely impaired by combinational pretreatment with mAbs in ICAM-1 and LFA-1 alpha. As shown in our previous report, the early appearance of CD3+TCR alpha beta- T cells, presumably TCR gamma delta T cells, was evident in the peritoneal cavity and liver of control rats at the early stage after listerial infection, while this was suppressed at this stage in rats pretreated with both 1A29 and WT1.(ABSTRACT TRUNCATED AT 250 WORDS)