The relative contribution of mast cell subsets to conjunctival T(H)2-like cytokines

PURPOSE. To investigate the distribution of the T-helper (T-H)2-like cytoki nes, interleukin (IL)-4, IL-5, IL-G, and IL-13 between mast cell subsets in conjunctival biopsy specimens from normal subjects and those with seasonal allergic conjunctivitis (SAC) during and outside of the grass pollen seaso n. METHODS. Sequential and double in situ hybridization (ISH) and immunohistoc hemistry (IHC) were performed on thin sections of human conjunctiva to dete rmine the colocalization of the immunoreactivity of IL-4 IL-5, IL-6, and IL -13 to mast cell subsets in normal subjects and subjects with atopy and to detect IL-4 mRNA in conjunctival mast cells. RESULTS. More than 90% of IL-4(+)-immunoreactive cells were observed to be mast cells in conjunctival biopsy specimens from all patient groups. The ma jority of IL-5(+), IL-6(+), and IL-13(+) cells were also noted to be mast c ells for each group. IL-4 preferentially colocalized to the tryptase-chymas e(+) mast cell phenotype (MCTC) with MCTC cells comprising 93.3% of cytokin e(+) mast cells in symptomatic SAC (P = 0.0017, 89.2% in asymptomatic SAC ( P = 0.0008), and 77.8% in normal subjects (P = 0.0472). IL-13 appeared to c olocalize preferentially to the MCTC phenotype and IL-5 and IL-6 to the MC, phenotype. ISH showed that 75.8% of mast cells in normal subjects, 78.7%: in subjects with symptomatic SAG, and 18.7% in subjects with asymptomatic S AC expressed mRNA for IL-4. CONCLUSIONS. Conjunctival mast cells are an important source of IL-4, IL-5, IL-6, and IL-13 immunoreactivity. with preferential colocalization of IL-4 and IL-13 on the MCTC subset and IL-5 and IL-6 to the MC, subset. This evi dence suggests that differences in protease phenotype may also reflect func tional differences evidenced by the different patterns of cytokine distribu tion.