CD4(+) v(alpha)14 NKT cells play a crucial role in an early stage of protective immunity against infection with Leishmania major.

The roles of gamma delta T, NK and NKT cells in an early stage of protective immunity against infection with Leishmania major were investigated. Further, the contribution of these innate cells to the expression of 65 kDa heat shock protein (HSP65) in host macrophages was examined, since we found previously that this expression prevents apoptotic death of infected macrophages and is a crucial step in the acquisition of protective immunity against infection with various obligate intracellular protozoa including L. major. C57BL/6 and DBA/2 mice were found to be resistant against the infection on the basis of the parasite burden in their regional lymph nodes, and to strongly express HSP65 in their macrophages, whereas BALB/c mice were susceptible and barely expressed the HSP65. In those resistant mice, CD4(+) NKT cells prominently increased in their regional lymph node and were the main effector cells at least for an early stage of the protective immunity and for the HSP65 expression, whereas this subset did not increase in susceptible BALB/c mice. Further, neither gamma delta T nor NK cells in resistant mice contributed to those protective immune responses. The NKT cell subset bore CD3, CD4, TCR alpha beta, IL-2R beta and NK1.1 but scarcely asialo-GM(1). Moreover, this effector subset was confirmed to be V(alpha)14 NKT cells by using J(alpha)281(-/-) mice.