Dissecting the hematopoietic microenvironment. III. Evidence for a positive short range stimulus for cellular proliferation.

Experiments were carried out with the intent of defining the nature of the microenvironmental defect which severely limits erythropoiesis in the spleen of the S1/S1d mouse. Chimeric spleens, half S1/S1d and half congenic +/+, supported erythropoiesis in the +/+ region but not in the S1/S1d region, regardless of which genotype was the irradiated, marrow-injected host animal. Implants of normal marrow stroma within the spleens of irradiated S1/S1d mice also supported normal proportions of erythrocytic and granulocytic hematopoiesis. Implants of normal spleen stroma, particularly the capsular portion, into unirradiated s1/s1d mice stimulated erythropoiesis originating from S1/S1d stem cells within and in the immediate vicinity of the implant. The evidence suggests a short range, stromal erythropoietic stimulatory factor which is lacking in the S1/S1d.