Corticotropin-releasing factor receptor 1 in mouse spleen: Expression after immune stimulation and identification of receptor-bearing cells

A specific polyclonal Ab against the N-terminal domain of corticotropin- releasing factor (CRF) receptor, type 1 (CRF-R1), was employed to an immunohistochemical analysis of the spleen from naive mice and mice exposed to an immune challenge. Cell types stained with anti-CRF-R1 Ab were identified by their nuclear shapes and colocalization with the cell type- specific markers ER-MP58, ER-MP20, Moma-1, Moma 2, anti-CD3e mAbs, and anti- Ig Ab. Only a few clusters of CRF-R1⁺ cells were found in spleen sections of naive mice at sites typical for granulopoietic islands. However, a 17-fold increase in the mean number of CRF-R1⁺ cells was noted within hours following a challenge of acute systemic inflammation induced by i.p. administration of LPS. The majority of these cells were identified as mature neutrophils. CRF-R1 was shown to mediate suppression of the IL-1β secretion by these cells. However, at later time points a large number of granulocyte- macrophage precursors was strongly labeled with anti-CRF-R1 Ab. Western blot analysis of splenic membranes from animals treated with LPS revealed a m.w. of approximately 70,000 for CRF-R1. Subcellular staining patterns were suggestive for the predominant localization of CRF-R1 on granule membranes. CRF-R1 mRNA was detected in spleen but not in bone marrow and peripheral blood leukocytes from naive mice. Thus, it was indicated that CRF-R1 was not produced constitutively by mature or immature neutrophils. Its production was rather triggered by inflammatory stimuli.