Positive selection of NKT cells by CD1(+), CD11c(+) non-lymphoid cells residing in the extrathymic organs.

Previously, we found that NK1.1(+), TCRalpha beta(+) natural killer T (NKT) cells develop in cytokine-supplemented suspension cultures of fetal liver established from normal, but not from beta2 microglobulin-deficient [beta2m(- / -)] mice, and that recombination-deficient SCID fetal liver can reconstiute NKT cell development in beta2m(- / -) fetal liver cultures. We found here that cells of SCID adult liver, bone marrow, spleen and thymus were able to reconstitute NKT cell development in the former culture system with efficiency comparable to normal thymic cells. The reconstitution of NKT cells was also seen in the bone marrow chimeras that had been administered a combination of beta2m(- / -) and Rag-2(- / -) bone marrow cells. Development of NKT cells was hampered by depletion of CD11c(+) or CD11b(+) cells, but not by removal of B220(+) or Gr-1(+) cells from cultures of normal fetal liver cells. Furthermore CD11c(+), CD11b(+) and / or CD11c(+) CD11b(-) cells (both populations were CD1-dull positive) enriched from Rag-2-deficient fetal livers and pulsed with alpha-galactosylceramide, a possible antigen for NKT cells, were shown to reconstitute the NKT cell development in beta2m(- / -) fetal liver cultures. Collectively, our findings suggest that non-lymphoid cells, presumably CD11c(+), CD11b(+) and / or CD11c(+), CD11b(-) dendritic cells, are involved in the mechanism of positive selection of NKT cells in the thymus and extrathymic organs.