The route of transfer determines the fate of differentiating plasma blasts. (A-B) Five days after intraperitoneal immunization with CT, splenocytes were isolated and adoptively transferred into individual recipients either by intravenous or intraperitoneal injection. Seven days after adoptive transfer, the number of adoptively transferred CT-specific antibody-secreting cells (ASC) present in the recipients' spleens and small intestinal lamina propria was determined by ELISPOT assay. Bars depict the mean number of CT-specific IgM-secreting cells in the spleen (A) and CT-specific IgA-secreting ASCs in the lamina propria (B) observed in 6 mice in 2 independent experiments. (C-D) Ly5.1⁺ wild-type splenocytes were injected either intraperitoneally (▩) or intravenously (□) into separate congenic Ly5.2⁺ recipients. One day (C) and 5 days (D) after transfer, the recipients' intestines were embedded as “Swiss rolls,” and the number of transferred cells present in the lamina propria was determined by immunofluorescence microscopy. Sections were stained with anti-Ly5.1, anti-IgM, and anti-IgA antibodies. The frequency of cells is expressed as number of cells observed per millimeter of length of the intestine analyzed. For each time point and route of transfer, at least 20 cm of intestine obtained from 3 independent recipients was examined. Error bars represent SEM.