in humans, three highly homologous, strictly tissue and locale specific isoforms have been identified: i-, t- and l-fimbrin. l-fimbrin is found in only normal or transformed leukocytes where it becomes phosphorylated in response to other factors such as interleukin-1. i-fimbrin is expressed by intestine and kidney epithelial cells. t-fimbrin is found in epithelial and mesenchymal cells derived from solid tissue where it does not become phosphorylated. differences in expression, sequence and phosphorylation among the various fimbrin isoforms suggest the likelihood of functional differences.