Activation of Human Peripheral Blood Lymphocytes: Effect of Concanavalin A and Lipopolysaccharide on in Vitro Synthesis of DNA and Immunoglobulins

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Abstract
We studied the Interaction of lipopolysaccharide (LPS) and concanavalin A (Con A) with regard to IgM and IgG production in in vitro cultures of human peripheral blood lymphocytes (PBL) In our system LPS alone over a wide range Of concentration did not stimulate detectable IgM or IgG production, while Con A at optimal (6 μg ml) and suboptimal (0.6 μg/ml) mitogen concentration induced synthesis of small amounts of Ig. A marked enhancing effect was present when both Con A and LPS were added to the cultures. The different doses of LPS had similar effect on both classes of Ig, and typical dose-response curves were obtained. To evaluate the cellular basis of this synergism, the effect on cell proliferation was studied undo identical experimental conditions in normal subject and patients with X-linked agammaglobulinaemia (X-LA). Parallel cultures were set up after monocyte depletion by adherence on petri dishes. On day 3, increasing doses of LPS were associated with progressive decreases in 3H-thymidine (3H-TdR) Incorporation. Similar result were obtained with normal lymphocytes and those from X-LA patients. Monocyte depletion did not substantially after the lymphocyte response pattern. The preferential Induction of helper activities, either directly by helper stimulation or indirectly by suppressor minimum, is suggested us a possible mechanism of the Interaction observed.