The porphyrin photosensitizer Photofrin elevates murine splenic erythropoiesis.

Changes occurring within the spleens of the genetically distinct DBA/1 and DBA/2 mouse strains produced by the photosensitizer Photofrin in the absence of direct light exposure were analyzed. Photofrin significantly increased spleen weight, cellularity and erythroid progenitor levels in both mouse strains tested. The expression of heat stable antigen (HSA), a marker present upon different immature leukocytes as well as certain fully-differentiated cell types including erythrocytes, was increased in the spleens of mice given Photofrin. It was shown for Photofrin-injected DBA/1 mice that a spleen cell population which expressed high levels of HSA also bound the iron transport protein transferrin. Photofrin increases the splenic demand for iron by promoting erythropoietic activity within the tissue.