Differentiation and activity of mast cells following immunization in cultures of lymph-node cells.

An extensive clonal differentiation into mast cells from primitive blast cell precursors occurred when lymph node cells obtained from mice immunized with horse serum were cultured on mouse embryonic skin monolayers. Horse serum was always present in the culture as a constituent of the nutritional medium. Mast cells developed to lesser extent also in cultures prepared from non-immunized mice. However, a clear difference in mast cell-granule ultrastructure and in histamine content was noted between the two. In cultures of lymph nodes cells from non-immunized mice the granules were tiny and uniform in size and in staining density; whereas granules in the immune cultures were larger and non-uniform in size and in staining density, and the intragranular organization manifested alterations of various forms. The content of intracellular histamine per 10(6) mast cells was about equal in both cultures. However, much more free histamine (per 10(6) mast cells) gradually accumulated in cultures of the immune lymph node cells, indicating higher rates of synthesis and release of histamine. The mast cells were readily degranulated by heat-inactivated (IgG1) sera of the mice used as donors of the lymph node cells. 92% of the mast cells were degranulated and as much as 80% of the histamine was released. The degranulation was accompanied by an immediate (albeit reversible) response of the fibroblast cells in the monolayer. A shift of the well-stretched cytoplasm of the fibroblasts opened numerous 'window' over the whole monolayer. The degranulated mast cells survived the process and could be maintained further in the cultures. Moreover, they were capable of repeated degranulation, releasing 50% of their histamine, even after four degranulation cycles performed over a 7 days' period of culture. No cytotoxic effect on the mast cells was noted and the histamine content in culture, 3 days after degranulation, seemed to be higher than in the undergranulated control cultures--suggesting an intensified rate of histamine synthesis.