Requirements for Bone Marrow–Derived Antigen-Presenting Cells in Priming Cytotoxic T Cell Responses to Intracellular Pathogens

Bone marrow (BM)-derived antigen-presenting cells (APCs) are potent stimulators of T cell immune responses. We investigated the requirements for antigen presentation by these cells in priming cytotoxic T lymphocyte (CTL) responses to intracellular bacterial and viral pathogens. [Parent→F₁] radiation BM chimeras were constructed using C57BL/6 donors and (C57BL/6 × BALB/c)F₁ recipients. Infection of chimeric mice with either Listeria monocytogenes or vaccinia virus expressing the nucleoprotein (NP) antigen from lymphocytic choriomeningitis virus (LCMV) primed H2-D^b–restricted, but not H2-K^d–restricted CTL responses, demonstrating the requirement for BM-derived APCs for successful priming of CTL responses to these pathogens. Surprisingly, this did not hold true for chimeric mice infected with LCMV itself. LCMV-infected animals developed strong CTL responses specific for both H2-D^b– and H2-L^d–restricted NP epitopes. These findings indicate that in vivo priming of CTL responses to LCMV is remarkably insensitive to deficiencies in antigen presentation by professional BM-derived APCs.