BONE-MARROW-DERIVED MACROPHAGE LINES AND IMMORTALIZED CLONED MACROPHAGE AND DENDRITIC CELLS SUPPORT PRIMING OF BORRELIA-BURGDORFERI - SPECIFIC T-CELL RESPONSES IN-VITRO AND OR IN-VIVO/

In vitro propagated bone marrow-derived macrophage populations (BMMO) as well as cloned immortalized macrophage (MT2/1) and dendritic (D2SC/ 1) cell lines were analyzed for their capacity to promote activation a nd/or proliferation of naive T cells to Borrelia burgdorferi antigens in vitro and in vivo. All three cell types constitutively express high levels of MHC class I structures as well as the co-stimulatory molecu les B7/BB1 and heat-stable antigen (HSA); MHC class II molecules (I-A) are upregulated following incubation with either intact spirochetes o r the purified lipoprotein OspA (Lip-OspA) but not with its delipidate d form (MDP-OspA). Only BMMO were able to induce proliferation of naiv e T cells or T cells derived from infected mice to intact spirochetes in vitro. However; all three accessory populations could support prima ry and secondary T cell responses to Lip-OspA but not, or only margina lly, to MDP-OspA under similar conditions, The number of accessory cel ls require for optimal stimulation of naive or pre-sensitized T cells was approximate to 3 x lower for D2SC/1 than for BMMO or MT2/1. In add ition, BMMO pre-pulsed with Lip-OspA were able to prime T cells in viv o, indicating a crucial role for the lipid moiety in antigen presentat ion, From two truncated lipopeptides of Lip-OspA containing either 20 or 6 aminoterminal residues, only Lip-OspA(pep20) but not Lip-OspA(pep 6) induced significant proliferation in naive or pre-sensitized T cell s in vitro, suggesting that T cells mainly respond to the protein rath er than the lipid moiety of OspA. Thus the data demonstrate that BMMO, MT2/1 and D2SC/1 have differential capacities to prime spirochete-rea ctive T cells and to support their growth in vitro, suggesting that op timal activation and propagation of T cells also depends on the qualit y of the antigen.