Expression of the costimulatory molecule CD28 and cytokines by mast cells

Cytokine expression by murine bone marrow-derived mast cells in response to interleukin-3 (IL-3) treatment and CD28 ligation was investigated. Cytokine uptake and cell-to-cell interactions via cell surface molecule ligations are two factors that may play an important role in how the microenvironment can affect the function and development of resident cells. IL-3, a mast cell growth factor, was observed to affect the cytokine profile of mast cells, and CD28, when crosslinked at the surface of mast cells along with a costimulus, was also observed to affect the cytokine profile of mast cells. Transcript analysis via Reverse Transcriptase-Rapid Polymerase Chain Reaction (RT-RPCR) demonstrated that IL-3 treatment of Stem Cell Factor (SCF)-derived bone marrow mast cells causes an increase in the level of IL-13 transcripts within 30 min and IL-10 transcripts within 1.5 hr. FACscan analysis using intracellular staining indicated that IL-3 derived bone marrow mast cells constitutively express IL-10. FACscan analysis also revealed that SCF-derived bone marrow cells express IL-10 4 days after IL-3 treatment. FACscan analysis also demonstrated that CD28 is expressed constitutively at low levels by IL-3-derived bone marrow mast cells and also expressed at higher levels by SCF-derived bone marrow mast cells at the cell surface after treatment with phorbol myristate acetate (PMA) or either of the bacterial products, lipopolysaccharide (LPS) or the Borrelia burgdorferi-derived outer surface lipoprotein, OspA. Transcript analysis via RT-RPCR determined that crosslinking of CD28 alone at the surface of the IL-3-derived bone marrow mast cells led to an increased level of c-jun transcripts but not c-fos transcripts. Transcript analysis via RT-RPCR also revealed that, with SCF-derived bone marrow mast cells, crosslinking of CD28 simultaneously with treatment of PMA led to increased levels of IL-13 transcripts. These results indicate that mast cells are capable of expressing CD28 and that some portions of the mast cell CD28 signaling pathway are similar to the T cell CD28 signaling pathway. Together, these results demonstrate that mast cells are capable of changing their cytokine profile in response to at least two stimuli within their microenvironment, cytokine uptake (IL-3) and cell surface molecule ligation (CD28).