T‐dependent activation of resting B cells mediated by concanavalin A

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Abstract
In cultures containing long-term cultured lines of antigen-specific helper T (Th) cells, normal unprimed B cells and concanavalin A (Con A), induction of B cells to immunoglobulin secretion and DNA synthesis was observed. The plaque-forming cell (PFC) response was large (frequently > 75000 PFC/106 input B cells) demonstrating the polyspecific nature of the response. Con A-mediated maturation and induction to DNA synthesis of responding B cells was completely Th cell dependent and inhibited with methyl-α-D-mannoside. Both resting and blasted B cells, separated by Percoll density centrifugation were induced to DNA synthesis and immunoglobulin secretion. Responses were completely unrestricted by the B cell major histocompatibility complex, even at the level of the resting B cell. The polyclonal nature of the response taken together with the Con A-mediated bypassing of T cell specificity and restricting haptotype indicates that this response is analogous to lectin-mediated cytotoxicity.