Search

Intravenous injection of goat antibodies to mouse IgD (GAMD) into BALB/c mice has been shown to induce vigorous T-cell dependent immunoglobulin responses, particularly of the IgGI and IgE isotypes. We have confirmed these findings and show that IgA responses are also triggered in this model. Since the study of IgE regulation in allergic individuals is concerned with secondary and subsequent T- and B-cell responses, we boosted GAMD-primed mice with goat antibodies to IgE or IgA in an attempt to specifically retrigger IgE- and IgA-bearing memory B cells. However, we found that secondary IgG1, IgE and lgA production could be elicited equally well by either antibody preparation or by normal goat IgG (GIg). As with the primary response, Gig primed and boosted mice produced very Iow or undetectable IgG1, IgE and IgA responses. These data suggest that GAMD is very efficient at priming T cells specific for Gig epitopes and that once primed they can be readily re-triggered by GIg. Spleen cells taken 7 days after boosting GAMD-primed mice were found to spontaneously produce much higher levels of interleukin-6 (IL-6) in culture than cells from unboosted or GIg primed and boosted mice. In contrast to primary responses, where IgE levels return to background (<40 ng/ml) very quickly, circulating IgE levels in boosted mice initially declined before reaching a plateau level (approximately 1 µg/ml) which was maintained for at least 148 days. IgG1 and IgA levels continued to fall over this same time period. Mice which had been primed (but not boosted) 10 months earlier were all found to have detectable IgE in their blood, despite the fact that following priming IgE becomes undetectable within 2-3 weeks. Since only a part of the IgE response was directed towards the antigen (GIg), these observations suggest the possibility that B cells initially primed to make IgE can be non-specifically retriggered in vivo. [ABSTRACT FROM AUTHOR]

Caco-2 cells grown on 0.45-micron filters, in Millicell chambers, form intact monolayers with many of the properties of polarized intestinal epithelial cells. It is reported here that these cells bind and internalize intrinsic factor-cobalamin complexes and that after 14-28 days in culture this specific binding is exclusively located on the apical membrane. Caco-2 cells also synthesize and secrete a protein with properties similar to transcobalamin II. This protein is secreted from the basolateral side of the cells after 20 days in culture. Specific apical-to-basolateral transcellular transport of [57Co]cobalamin also occurs between 20 and 28 days in culture. Thus, Caco-2 cells provide the first polarized human cell system for studying the transepithelial transport of cobalamin.