Béatrice Pérarnau

Single H2Kb, H2Db and double H2KbDb knockout mice: peripheral CD8+ T cell repertoire and antilymphocytic choriomeningitis virus cytolytic responses

Single H2Kb, H2Db and double H2KbDb homozygous knockout (KO) mice were generated and their peripheral CD8+ T cell repertoires compared to that of C57BL/6 (B6) mice. Limited (10 – 20 %, H2Db), substantial (30 – 50 %, H2Kb) and profound (90 %, H2KbDb) reduction of peripheral CD8+ T cells was observed in KO mice, without Vβ diversity alteration. Classical class Ia molecules therefore ensure most but not all of the peripheral CD8+ T cell repertoire education. As expected, H2Kb but also H2Db KO mice developed choriomeningitis following intracranial infection by lymphocytic choriomeningitis virus with the same kinetics, lethality and CD8+ cell implication as wild‐type B6 mice. By contrast, H2KbDb (class Ia–Ib+) KO mice survived. Choriomeningitis of H2Db KO mice was linked to the development of a subdominant (in normal B6 mice) H2Kb‐restricted cytotoxic T lymphocyte response. Mice expressing a restricted set of histocompatibility class I molecules should represent useful tools to evaluate the immunological potentials of individual MHC class I molecules.

Phenotypic characterization of CD8(+)NKT cells.

We describe a novel CD8+NKT cell population expressing TCRα /β or TCRγ /δ . These CD8+NKT cells were prominent in the liver, and except for the thymus, virtually absent in other lymphoid organs. CD8+NKT cells expressed activation markers and comprised a high proportion of Ly49+ cells. The development of the majority of CD8+NKT cells expressing TCRα /β, but not TCRγ /δ, depended on classical MHC class I. No CD8+NKT cells were detectable in young athymic mice, whereas the cells expressing TCRγ /δ, but not TCRα /β, appeared randomly in aged athymic mice. CD8+NK1+ TCRα /β cells showed polyclonal TCRVβ usage and were virtually devoid of TCRVα14. CD8+NK1+ TCRγ /δ cells predominantly expressed TCRVγ1, 2 and 4, and Vδ4, 5, 6 and 7. CD8+NKT cells, in particular those expressing TCRγ /δ, were a major population in early life. IFN‐γ, but not IL‐4, was induced in CD8+NKT cells by in vitro stimulation, independent of the TCRα /β or TCRγ /δ lineage. Hence, these cells represent a unique, though heterogeneous T cell population that shares markers with, but is distinct from, both conventional NKT cells and conventional CD8+ T cells, and that may play a role in immune regulation.

MHC class Ia-restricted T cells partially account for beta 2- microglobulin-dependent resistance to Mycobacterium tuberculosis

Recent studies have highlighted the heterogeneous nature of the CD8+ T cell response during human Mycobacterium tuberculosis infection; MHC class Ia, MHC class Ib and CD1 have all been identified as significant restriction elements. Here we have attempted to define the role of MHC class Ia in resistance to M. tuberculosis infection in mice. The course of M. tuberculosis infection in mice deficient in a single MHC class Ia molecule, either H2‐Kb or H2‐Db, was essentially identical to that observed in wild‐type mice. In contrast, mice fully deficient in MHC class Ia molecules (H2‐Kb / H2‐Db double knockout mice) were substantially more susceptible to M. tuberculosis infection. However, the double knockout mice were not as susceptible as β 2‐microglobulin‐deficient mice, which have a broader phenotypic deficit. Thus, antigen presentation via MHC class Ia is an important component in resistance to M. tuberculosis, but its absence only partially accounts for the increased susceptibility of β 2‐microglobulin‐deficient mice.

MHC class Ia molecules alone control NK‐mediated bone marrow graft rejection

Mice with functionally deleted genes encoding MHC class I heavy (H‐2Kb, H‐2Db) and light (β2‐microglobulin) chains were used in bone marrow cell transfer experiments to study the role of class Ia and Ib molecules in NK cell function. Absence of H‐2Kb and absence of H‐2Db on bone marrow cells resulted in complete and in almost complete NK‐mediated rejection, respectively. Absence of either H‐2 class Ib (at least when expressed in H‐2 class Ia‐deficient mice) or cell surface class Ia free heavy chains did not result in bone marrow rejection. Thus, in C57BL / 6 adult mice, the inactivation of NK cells required for bone marrow cell engraftment relies entirely upon‐H‐2 class Ia molecules. These results imply the existence of an inhibitory receptor which recognizes either directly or indirectly H‐2Db molecules and further suggest that in C57BL / 6 mice the NK cells which do not express a H‐2Kb specific inhibitory receptor necessarily express an H‐2Db‐specific one.

H-2D b−/− Mice Are Susceptible to Persistent Infection by Theiler's Virus

ABSTRACT H-2b mice are resistant to persistent infection of the central nervous system by Theilers virus. They clear the infection 7 to 10 days after intracranial inoculation. Resistance maps to the H-2D gene and not to the H-2K gene and is associated with a potent antiviral cytotoxic T-lymphocyte (CTL) response. We used H-2b mice in which theH-2D or the H-2K gene had been inactivated to dissect the respective roles of these genes in resistance. We report that H-2D−/− but notH-2K −/− mice were susceptible to persistent infection. Furthermore, whereas H-2K −/−mice mounted a vigorous virus-specific CTL response, similar to that of control C57BL/6 mice, the CTL response ofH-2D −/− mice was nil or minimal. Using target cells transfected with the H-2Db or theH-2Kb gene, we showed that theH-2K-restricted CTL response against the virus was minimal in H-2D −/− mice. These results demonstrate that the H-2Db andH-2Kb genes play nonredundant roles in the resistance to this persistent infection.