Mechanisms of macrophage stimulation through CD8: macrophage CD8alpha and CD8beta induce nitric oxide production and associated killing of the parasite Leishmania major.
Prior studies demonstrated that rat macrophages express CD8, which differs from T lymphocyte CD8 within the ligand binding domain. We investigated whether stimulation of macrophage CD8 could induce mediator release and regulate host defense. Cross-linking either CD8alpha (OX8, 5 microg/ml) or CD8beta (341, 10 microg/ml) stimulated nitric oxide (NO) production, which correlated with an up-regulation of inducible NO synthase protein. Cell signaling inhibitors were used to elucidate the pathways of CD8alpha and CD8beta stimulation. Genistein (broad spectrum protein tyrosine kinase inhibitor, 10 microg/ml), PP1 (src family kinase inhibitor, 5 microg/ml), polymyxin B (protein kinase C (PKC) inhibitor, 100 microg/ml), and Ro 31-8220 (PKC inhibitor, 1 microM) significantly inhibited anti-CD8alpha- and anti-CD8beta-stimulated NO production and inducible NO synthase up-regulation, suggesting that tyrosine kinase(s) (src family) and PKC are involved in CD8 signaling. In addition, cross-linking CD8alpha stimulated NO-dependent macrophage killing of the parasite Leishmania major. For the first time, this work demonstrates that the beta-chain of macrophage CD8, in addition to the alpha-chain, can regulate mediator release. These results further illustrate the importance of this molecule and support our previous data demonstrating differences between macrophage and T lymphocyte CD8. Additional studies on the signaling mechanisms and possible ligand(s) for macrophage CD8 will lead to a greater understanding of inflammation and host defense.
Hirji
N
N
Department of Medicine, University of Alberta, Edmonton, Canada.
Lin
T J
TJ
Bissonnette
E
E
Belosevic
M
M
Befus
A D
AD
D000818:Animals; D016827:CD8 Antigens / Q000276:immunology*; D018320:Leishmania major / Q000276:immunology*; D008262:Macrophage Activation; D016676:Macrophages, Alveolar / Q000201:enzymology / Q000276:immunology* / Q000469:parasitology; D008297:Male; D009569:Nitric Oxide / Q000096:biosynthesis*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D051381:Rats; D017207:Rats, Sprague-Dawley; D015854:Up-Regulation; D019061:src-Family Kinases / Q000378:metabolism
D016827:CD8 Antigens; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D019061:src-Family Kinases