Surface CD88 functionally distinguishes the MCTC from the MCT type of human lung mast cell

Abstract

Background: MC(T) and MC(TC) types of human mast cells (MCs) are distinguished from one another on the basis of the protease compositions of their secretory granules, but their functional and developmental relationships have been uncertain.

Objective: These studies better define the functional properties and developmental relationship of MC(T) and MC(TC) cells.

Methods: Mast cells were dispersed from human skin and lung, purified with anti-Kit antibody, and separated into CD88+ and CD88- populations by cell sorting. These cells were evaluated by immunocytochemistry with antitryptase and antichymase mAbs; for chymase and tryptase mRNA by real-time RT-PCR; for conversion of MC(T) to MC(TC) cells during cell culture with recombinant human stem cell factor and recombinant human IL-6; and for degranulation and leukotriene C 4 (LTC 4 ) secretion when stimulated with anti-FcepsilonRI, substance P, C5a, and compound 48/80.

Results: Mature MC(T) and MC(TC) cells were separated from one another on the basis of selective expression of CD88, the C5aR, on MC(TC) cells. Lung MC(T) cells had negligible levels of chymase mRNA and retained their MC(T) phenotype in culture. Mature MC(TC) cells from skin and lung degranulated in response to FcepsilonRI cross-linking, C5a, compound 48/80, and substance P. Lung MC(TC) cells released LTC 4 on activation, but no LTC 4 was detected when skin-derived MC(TC) cells were activated. MC(T) cells from lung degranulated and released LTC 4 in response to anti-FcepsilonRI and substance P, but not to C5a and compound 48/80.

Conclusion: These observations functionally distinguish MC(T) from MC(TC) types of human mast cells and suggest important differences that may affect their participation in diseases such as asthma and urticaria.

FIG 1.

Purification and separation of MC_TC and MC_T cells from Lu-MC. Mast cells were labeled with rabbit anti-CD88/Alexa 488-goat antirabbit IgG and phycoerythrin-mouse anti-Kit mAb and sorted by flow cytometry. Sorting gates are shown by the gray polygons. Sorted cells were cultured overnight and subjected to analytical flow cytometry (lower panels) or cytocentrifugation and immunocytochemistry with antichymase mAb.

FIG 2.

Activation profiles of purified MC_T and MC_TC cells from different sources. Cells (10⁶/mL) were exposed to anti-Fc∊RI, C5a, compound 48/80, and substance P for 2 hours at 37°C. Net percent release of β-hexosaminidase (left panels) and net release of sulfidopeptide LTs (right panels) were determined. Overall, spontaneous release values for β-hexosaminidase were ≤6.5% and for LTC₄/D₄/E₄ were undetectable.

FIG 3.

Effect of IL-6 on chymase protein expression in Lu-MC. Cytospins of purified lung-derived mast cells were stained with antichymase or antitryptase mAbs. The staining intensities of positive cells from 3 different lung mast cell preparations were then measured by image analysis. For each preparation, 10 to 15 chymase⁺ and 12 to 20 tryptase⁺ mast cells were examined. ^*P < .05 compared to no IL-6.