The appearance in mice of specific antibody within newly formed germinal centers in lymph nodes was demonstrated by light and electron microscopy after regional primary antigenic stimulation with horseradish peroxidase (HRP).

Lymphoid germinal center cells containing anti-HRP antibody in the perinuclear space and in the cytoplasm were detected from 17 to 26 days after antigenic stimulation. Extracellular anti-HRP antibody within germinal centers, localized between dendritic reticular cells and lymphoid elements, could not be found before the appearance of intracellular antibody. These findings strongly suggest antibody formation by lymphoid germinal center cells. Both antigen and corresponding antibody persisted in intercellular spaces up to 35 days after primary stimulation.

The concomitant presence in a given lymph node of germinal centers which are positive or negative with regard to specific antibody provide evidence in favor of monospecificity of individual centers. The mechanisms of antigen-trapping within germinal centers are discussed in the light of the present observations.

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