Zonal distribution of immunoglobulin-synthesizing cells within the germinal centre: an in situ hybridization and immunohistochemical study.

Immunohistologic studies have shown that synthesis of cytoplasmic immunoglobulin (cIg) is a normal function of some follicle centre cells (FCCs). The mechanisms regulating this synthesis of immunoglobulin and its function within the germinal centre are still poorly understood. In this study we applied a recently developed in situ hybridization method for the detection of kappa and lambda light chain mRNA to reactive lymph nodes and tonsils in order to investigate further the immunoglobulin-synthesizing cells of the germinal centre. FCCs containing detectable levels of light chain mRNA corresponded closely to cells containing cIg. The detection of light chain mRNA rather than its immunoglobulin product was found to be an advantage in that problems associated with the detection of extracellular immunoglobulin were eliminated. This was most apparent in germinal centres where the absence of 'network' immunoglobulin led to the observations that immunoglobulin-synthesizing FCCs are predominantly small centrocytes and that in a proportion of germinal centres they localize in that part of the light zone closest to the dark zone. This zonal distribution of immunoglobulin-synthesizing FCCs raises the possibility of further functional and micro-environmental subcompartments within the light zone.