The phenotype and fate of the antibody‐forming cells of the splenic foci

TLDR

The initial humoral response generates low‑affinity antibodies from extrafollicular antibody‑forming cells in spleen and lymph node, which proliferate rapidly but decline sharply, leaving few cells after 14 days. The study aimed to isolate and characterize antigen‑specific AFC by flow cytometry to identify markers distinguishing them from germinal center B cells. The authors isolated AFC by flow cytometry and used ELISpot assays to show that their rapid decline was not due to migration to bone marrow. At day 7, AFC expressed low B220, high syndecan, and surface IgG1, and their decline was attributed to in‑situ apoptosis confirmed by nick‑end labeling.

Abstract

Abstract The first product of the humoral response to antigen is low‐affinity antibody, produced by extrafollicular foci of antibody‐forming cells (AFC) in organs such as spleen and lymph node. These cells proliferate rapidly but then undergo an equally rapid decline, so that they are present in only small numbers 14 days after immunization. We have used 6‐parameter flow cytometry to isolate and examine the characteristics of (4‐hydroxy‐5‐nitrophenyl)acetyl‐specific AFC, looking in particular for those markers that might differentiate them from cells of the intrafollicular (germinal center) arm of the T‐dependent immune response. At day 7 of the primary response, most AFC were found to express surprisingly low levels of B220, high levels of syndecan, and retain significant levels of surface IgG1. We then used enzyme‐linked immunospot assays to demonstrate that the rapid decline of these cells was not likely to be due to migration to organs such as the bone marrow. Their decline could, however, be explained by apoptosis in situ , which was demonstrated immunohistologically by nick‐end labeling.