Thymus and lymph node cells (LNC) from male Lewis and BN rats of exactly the same age were evaluated for 3HTdR incorporation in culture after stimulation with the mitogens concanavalin A (Con A), phytohemagglutinin (PHA), or Escherichia coli lipopolysaccharide (LPS) over a 1000-fold dose range, and after mixed lymphocyte culture (MLC) with (Lewis × BN)F1 LNC. BN thymus cells stimulated by mitogens or by histocompatibility antigens of hybrid LNC in MLC can incorporate as much 3HTdR as Lewis thymocytes under identical culture conditions. Lewis and BN thymus cells respond identically to PHA or in MLC, and neither type of thymus cell responds to LPS in culture. The only difference observed between lewis and BN thymus cells was that BN cells required 4-fold higher concentrations of Con A to produce a maximal DNA synthetic response. Lewis LNC were superior to BN cells in terms of Con A or PHA stimulated DNA synthetic responses irrespective of mitogen concentration. The strain specific Con A concentration difference noted for thymus cells was also present in cultures of LNC. Lewis LNC responded better than BN LNC under identical MLC conditions with LBNF1 cells. LPS stimulation of DNA synthesis was identical for Lewis and BN LNC. These observations indicate that Lewis and BN thymus dependent (T)-cells differ in at least two parameters: 1) a Con A concentration dependent reactivity irrespective of their location, and 2) a potential for in vitro DNA synthesis by mature, peripheralized T cells from the lymph nodes.

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