MHC CLASS IB-RESTRICTED CELLS CONTRIBUTE TO ANTILISTERIAL IMMUNITY - EVIDENCE FOR QA-1(B) AS A KEY RESTRICTING ELEMENT FOR LISTERIA-SPECIFIC CTLS

Subclinical infection of BALB/c mice with the intracellular pathogen L isteria monocytogenes results in the development of MHC class Ia-and i b-restricted CTLs. L. monocytogenes-infected TAP-'-bone marrow macroph age targets are not lysed by MHC class la-or Ib-restricted CTLs, showi ng a requirement for transport of peptides into the endoplasmic reticu lum for development of the MHC class Ib-peptide target. L. monocytogen es-infected B6.Tla(a)-derived bone marrow macrophages (K-b Qa-1(a)) ar e not lysed by BALB/c (K-d Qa-1(b))-derived antilisterial CTLs, confir ming an earlier finding that the Ib-restricting element is T region en coded. We have further determined that Qa-1(b) is a restricting elemen t for antilisterial CTLs using L. monocytogenes-infected Qa-1(b)-trans formed mouse L cells as well as human-derived HeLa cells as target pop ulations. These L. monocytogenes-infected Qa-1(b)-transformed cell lin es are lysed by BALB/c (Qa-1(b))- or C57BL/6 (Qa-1(b))-derived antilis terial CTLs, but are not lysed by B6.AKM (Qa-1(a))-derived antilisteri al CTLs. Using L. monocytogenes-infected targets, we found that MHC cl ass la-and Ib-restricted CTLs are evident within 4 days following infe ction, peak on day 5 following infection, and although Ib-restricted C TLs disappear by day 6 postinfection, la-restricted antilisterial CTL activity can still be detected. These results demonstrate that Qa-1(b) is a restricting element for antilisterial CTLs, and expression of th e MHC class Ib-presented target at the cell surface is TAP dependent, In addition, these results show that following L. monocytogenes infect ion, MHC class Ib-restricted CTLs are evident in vivo.