Macrophage heterogeneity generated by differential gene expression

Macrophages (mos) exist as functionally heterogeneous populations. Mos derived from bone marrow precursor cells using either colony-stimulating factor-1 (CSF-1) or granulocyte/macrophage colony-stimulating factor (GM-CSF) have been studied to determine the distinct functional phenotypes both constitutively and after stimulation. In the present study, mo heterogeneity was examined by a subtraction cDNA library to identify genes differentially expressed by distinct mo populations constitutively and after activation by IFN-$\gamma.$ Cultures of bone marrow-derived mos were treated with 50 U/ml IFN-$\gamma$ for 40, 70 and 140 min to induce or enhance expression of early responsive genes regulated by IFN-$\gamma,$ and these stimulated mos were pooled. Poly(A)$\sp+$ RNA was prepared from both unactivated and IFN-$\gamma$-stimulated mos, and cDNA libraries were constructed in ZAP-II. Genes commonly expressed by both untreated and activated mo populations were removed by subtraction using biotin-avidin precipitation of hybrid complexes. Further selection was performed using differential screening of cDNAs prepared from mRNA from unactivated mos, followed by colony hybridization to remove sister clones.Of 31 clones randomly selected from the subtraction library, five clones showed intrinsic differential expression between GM-CSF- and CSF-1-derived mos, and another five clones revealed induced or enhanced expression by IFN-$\gamma$ in GM-CSF-derived mos. In CSF-1-derived mos, these ten cDNA clones were either not expressed (GM2B1 and the small RNA species of GM3E1) or constitutively expressed (GM3A2, large mRNA species of GM3E1, GM4A12, GM2A12 and GM2B8). Four clones (GM3D7, GM1A2, GM1B4 and GM1F2) even showed reduced expression following IFN-$\gamma$ stimulation in CSF-1-derived mos. These cDNAs, except GM2B1 and GM3A2, were not significantly homologous with known DNA sequences, implying that they represent novel cDNAs differentially expressed by distinct mo populations before or after treatment with IFN-$\gamma.$ These data imply that the functional heterogeneity of bone marrow-derived mos (BMDMs) may be due to differential expression of as yet unidentified genes. Additional analysis of these cDNAs and their deduced amino acid sequences are discussed on the basis of the possible implication of these cDNAs in mo heterogeneity induced by different hematopoietic stimuli.U of I OnlyETDs are only available to UIUC Users without author permissio