The ability of macrophage-associated antigen to both prime for, and subsequently trigger, IgE responses in inbred rats and mice was investigated. Peritoneal exudate cells briefly pulsed in vitro with ovalbumin (PEC-OVA) served as the immunogen, and both primed and unprimed animals as recipients. The experiments revealed that the intraperitoneal administration of relatively small numbers of PEC-OVA, while generally ineffective in inducing primary IgE responses in immunologically virgin mice, successfully primed the latter for secondary IgE responses following later challenge. Furthermore, PEC-OVA was highly effective in triggering vigorous secondary IgE responses in primed mice, producing PCA titres up to 10,000 in both moderate and high IgE-responder strains. The data further indicate that the IgE response induced in mice by PEC-OVA is transient, it exhibits a markedly lower threshold (in both the primary and secondary response) than corresponding haemagglutinating antibody responses, and is MHC-restricted. In the rat strain employed (low IgE-responder WAG), PEC-OVA administration evoked vigorous haemagglutinating antibody responses in pre-immunized rats, and primed immunologically virgin animals for similar secondary responses. However, PEC-OVA was only weakly immunogenic/antigenic for IgE responses in WAG rats.
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