Partitioning of cell surface class ii expression and antigen presenting capacity of macrophages in an MHC‐GENE dosage model

Publisher Website
Google Scholar
Abstract
Antigen presentation requires intracellular processing of foreign antigens to generate immunogenic peptides displayed at the surface of antigen presenting cells (APCs) in the context of major histocompatibility complex (MHC) class II molecules. We compared Sephadex‐elicited chicken peritoneal macrophages containing either two (disomic), three (trisomic), or four (tetrasomic) copies of the microchromosome encoding the MHC for both quantitative cell surface expression of MHC class II antigens and antigen presentation ability. Using indirect immunofluorescence flow cytometry, an increased percentage of class II‐positive cells and elevated mean class II‐related fluorescence intensity was found among tetrasomic macrophages as compared to disomic controls harvested 4 hours after intraperitoneal (i.p.) Sephadex injection. At 42 hr post Sephadex, peritoneal exudate cells (PECs) from disomic and aneuploid (trisomic and tetrasomic) chickens were similar in the incidence of class II‐positive cells; however, more class II molecules were expressed on the surface of fluorescence‐positive aneuploid macrophages compared to disomic controls. Inflammatory macrophage class II expression was also measured by ELISA and standardized by the content of cellular protein. No statistically‐significant difference was evident among the three genotypes at the late (42 hr) stage of the inflammatory responses; however, for 24 hr post Sephadex cells, aneuploid adherent macrophages possessed significantly elevated class II levels compared with disomic controls. Antigen presentation ability was tested in vitro using antigen (BSA)‐exposed normal or aneuploid macrophages co‐cultured with BSA‐primed normal T lymphocytes sharing the same MHC haplotype (B15). Keyhole limpet hemocyanin (KLH) was used as an antigen control. Disomic macrophages were found to possess either similar (24 hr post Sephadex) or superior (42 hr post Sephadex) antigen presentation capacity compared with aneuploid macrophages. The results suggest that the level of macrophage class II expression is correlated with chicken MHC gene dosage; however, class II level is partitioned from antigen presenting capacity within this model.