Phenotype and frequency of cells secreting IL-2, IL-4, IL-6, IL-10, IFN and TNF-α in human peripheral blood

The phenotype and frequency of cells in normal human peripheral blood spontaneously secreting IL-2, IL-4, IL-6, IL-10, IFN and TNF-α ex vivo was determined using ELIspot assays. CD4⁺T cells were the dominant source of IL-2 and IL-4 while multiple cell types (primarily CD8⁺lymphocytes) produced IFN. Fewer than 0.05% of mononuclear cells were spontaneously secreting these T cell derived factors. By comparison, IL-6, IL-10 and TNF-α were produced by 0.7–20% of PBMC. The primary sources of the latter cytokines were CD14⁺macrophages/monocytes. A significant positive correlation was found in the frequency of cells secreting IL-6, IL-10 and TNF-α ex vivo, suggesting that the release of such factors was coordinately regulated. No such correlation was found among IL-2, IL-4 and IFN secreting cells, indicating that the production of predominantly T cell derived cytokines was regulated independently.