T and B cells have similar recirculation kinetics in sheep

T and B cells continually migrate around the body by recirculating between blood and lymph via lymphoid tissues. This is an important way of fostering the cell-cell interactions required for the initiation of an immune response. Data from previous studies of T and B cell recirculation, based on relatively complex approaches, have been interpreted as evidence that the recirculation of B cells is more sluggish than for T cells. We have shown from a study in sheep that this is not the case. Lymphocyte migration through both the intestine and the prescapular lymph node was analyzed by cannulating efferent lymphatics. The lymph cells were labeled in vitro with Hoechst 33342, or other fluorochromes, then injected i.v., and the rate of their recirculation into the lymph was determined by fluorescence microscopy. A multicolor immunofluorescence assay was used to classify each recirculated cell as either a T or B cell. This established that the T and B cells from intestinal lymph and from prescapular lymph recirculate with similar kinetics. The recovery of i.v. injected T and B cells was the same in prescapular lymph, but fewer injected B cells than T cells were recovered in intestinal lymph. Thus, although the recirculation kinetics are the same for T and B cells, the two populations are handled differently in intestinal tissues and a lymph node remote from the gut.