Analysis of thymus‐independent type 2 antigen uptake by marginal zone macrophages in thin slices of viable lymphoid tissue in vitro

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Abstract
There is evidence to suggest that the B cell population in the marginal zone (MZ) of the spleen is responsible for the antibody response to thymus‐independent type 2 antigens (TI‐2). The macrophage (MΦ) population in the MZ has been shown to take up TI‐2 antigens selectively, and this uptake is potentially important in understanding antigen handling in TI‐2 responses. Uptake has not been studied in vitro because isolation of MZ MΦ completely abrogates uptake. We have adapted a technique for cutting thin slices of viable spleen which retained this MΦ function under in vitro conditions and allowed manipulation of the system. This technique may have widespread application in the study of tissue MΦ which are difficult to isolate. Using this method, we show that MZ MΦ in splenic slices in vitro selectively take up a TI‐2 antigen, in a way apparently identical to that seen in vivo. This is not due to high pinocytic activity by these cells nor to their anatomical location. We provide evidence for a receptor‐mediated uptake system, whose function is sensitive to collagenase. The ligand specificity of the uptake system showed unexpected cross‐reactivity with the mannosyl‐fucosyl receptor with high affinity for mannan, but was not identical to it, and may be indicative of the natural ligands for the TI‐2 antigen uptake system.

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