Ultrastructure of eosinophils and basophils stimulated to develop in human cord blood mononuclear cell cultures containing recombinant human interleukin-5 or interleukin-3.

We used recombinant human interleukins (IL) and cultured human cord mononuclear cells to determine the cell lineages supported by the inclusion of the individual interleukins-5, -3, or -4 in the cultured media. Cultures were examined by electron microscopy at 2-, 3-, and 5-week culture intervals. We found that IL-5 primarily supported the eosinophilic lineage with lesser numbers of basophils, that IL-3 initially supported all granulocyte lineages but eventually supported the eosinophilic lineage with lesser numbers of basophils, and that IL-4 did not support the development of granulocyte lineages in these cultures. At early culture intervals in either IL-5 or IL-3, eosinophilic and basophilic myelocytes were seen in variable proportions. Mature cells of these lineages developed later. Both mature eosinophils and basophils showed morphologic evidence of activation similar to those described for tissue eosinophils and basophils in various disorders. Mast cells were absent in all cultures. Recognition of the variable morphologies associated with maturation and activation of human eosinophils and basophils is important for the correct identification of cell lineages that develop in cultures containing human recombinant interleukins.