Macrophage polarization in kidney transplant patients

Macrophages can oscillate between two functionally distinct states: proinflammatory M1 and anti-inflammatory M2. Classically- activated M1 macrophages produce proinflammatory cytokines (TNF-α, IFN-ƴ, and IL-6), which ares associated with graft dysfunction/rejections. In contrast, alternatively-activated macrophages M2 produce anti-inflammatory cytokines (IL-10) that are involved in host defense, tissue repair/remodeling, debris scavenging, and immune regulation, thereby helps to improve long-term graft survival.

In this study, we have identified graft dysfunction or rejection by biopsies using immunohistochemistry. Flow cytometry was used to detect M1 (CD163+, CD206+, and CD200R+) and M2 (CD86+, CD80+, and CD68+) macrophages. Enzyme-linked immunosorbent assay (ELISA) was used to measure a panel of cytokines.

Histological analysis of the kidney transplants (n = 30) was used to distinguish those with acute/chronic allograft rejection (n = 15) from those with stable kidney function (n = 15). Flow cytometry results showed that patients with graft rejection exhibited macrophages with decreased expression (33.28%) of M2 macrophage markers (CD163+, CD206+, and CD200R+) and reduced production of IL-10 (as detected using ELISA). However, 71.33% of the macrophages were found to have M1 markers (CD86+, CD80+, and CD68+; p = 0.002) and produced proinflammatory cytokines (TNF-α, IFN-ƴ, and IL-6) by ELISA (p = 0.001) when compared with the healthy control group. In contrast, stable kidney transplants had 65.58% M2 and 27.66% M1 macrophages (p = 0.03) and produced IL-10. These findings suggest that M1 macrophages dominate in kidney grafts with dysfunction or rejection, whereas M2 macrophages dominate in kidney grafts with stable function.

Our observations implicate a major shift towards M2 macrophages in stable kidney transplants, which are markedly downregulated in patients with graft dysfunction or rejection. In contrast, an increased frequency of M1 macrophages remained dominant in the pathophysiology of kidney transplants undergoing active dysfunction or rejection.