Ovine mast cell heterogeneity is defined by the distribution of sheep mast cell proteinase

The presence or absence of the granule chymase, sheep mast cell proteinase (SMCP), was determined in trachea, bronchus, bronchial lymph node, lung, thymus, spleen, liver, flank skin, abomasum, duodenum, jejunum, ileum, colon and mesenteric lymph node by immunohistochemistry and by enzyme-linked immunosorbent assay using a polyclona, affinity purified anti-SMCP antibody. Additionally, the presence of putative ovine mast cell subsets was investigated by comparing the number of mast cells identified histochemically (toluidine blue pH 0.5) with the number detected by immunostaining. The thymus had the greatest density of mast cells (225.7 ± 23.4 cells mm−2, histochemically) and the highest concentration of SMCP (19.7 ± 9.3 μg SMCP g−1 wet tissue). There was a high degree of correlation between toluidine blue and anti-SMCP cell cpunts for all tissues (r2 = 0.96, P < 0.001) with the exception of skin and liver. On the basis of reactivity to the anti-SMCP antibody, two populations of mast cells were defined, notably those in gastrointestinal tissues (analogous to the mucosal mast cell subset) and those present in skin (the putative ovine connective tissue mast cell subset). Ovine mast cell heterogeneity, resulting from differential expression of SMCP, was thus confirmed.