Mouse mutants and experimental outline to assess mast cells in normal and inflamed skin. (A) Genotypes and their impact on lymphocytes (T cells, B cells, NK cells) and on mast cells are indicated. The generation of new compound mutants is explained in the text. (B) Experimental outline. Mice were treated topically on one ear with PMA in acetone and on the contralateral ear with acetone (solvent) alone 3 times per week. Ear thickness was measured in regular intervals (see Figure 3) during the course of the treatment. After 6 weeks, numbers of mast cells in the ears were determined histologically.