Several adherent cell lines that express surface Ia antigens have been cloned from the P388 leukemia. These cell lines express many morphological and functional similarities to dendritic cells of the spleen. Adherent clones express H-2 gene products from the I and D regions, but do not possess Fc or C3b receptors or surface Ig. The cytoplasm of the adherent P388 clones has an abundance of mitochondria but few phagolysosomes. The adherent clones all strongly stimulate the proliferation of syngeneic or allogeneic T lymphocytes in the absence of antigen; however, cytotoxic T cells directed against the stimulators are induced only during allogeneic stimulation. Nonadherent clones of P388, which also express Ia antigens, do not stimulate either allogeneic or syngeneic T cell proliferation. The isolation of Ia-bearing adherent cell lines makes it possible to study Ia-mediated events in both antigen-dependent and independent immune systems using homogeneous accessory cell populations.

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