May play a role in the regulation of T and B-lymphocyte development and signal transduction. H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate Inhibited in cells after FCER1A triggering. Oxidized at active site cysteine. Treatment with pervanadate (vanadate and H(2)O(2)) or with antigen enhanced oxidation of active site cysteine. Belongs to the protein-tyrosine phosphatase family. Non-receptor class subfamily.