Macrophage infiltration of the kidney is a prominent feature associated with the severity of renal injury and progressive renal failure. To determine the influence of macrophages in renal disease models in the absence of endogenous T and B cells, we performed adoptive transfer of macrophages into severe combined immunodeficient (SCID) mice. In this study, macrophages were isolated from the spleens of BALB/c mice and stimulated with lipopolysaccharide to induce classically activated M1 macrophages or with interleukin-4 (IL-4) and IL-13 to induce alternatively activated M2 macrophages. These macrophages were then infused into SCID mice with adriamycin nephropathy; an in vivo model of chronic inflammatory renal disease analogous to human focal segmental glomerulosclerosis. Mice infused with M1 macrophages had a more severe histological and functional injury, whereas M2 macrophage-induced transfused mice had reduced histological and functional injury. Both M1 and M2 macrophages localized preferentially to the area of injury and maintained their phenotypes even after 4 weeks. The protective effect of M2 macrophages was associated with reduced accumulation and possibly downregulated chemokine and inflammatory cytokine expression of the host infiltrating macrophages. Our findings demonstrate that macrophages not only act as effectors of immune injury but can be induced to provide protection against immune injury.

Programmed death 1 (PD-1) is a novel member of the CD28/cytotoxic T-lymphocyte-associated protein-4 superfamily, which plays an important role in the regulation of activated T cells. However, it is not clear how PD-1 is expressed in normal and diseased kidney, nor if it has a role in progression of chronic renal disease. PD-1 expression and the effect of monoclonal anti-PD-1 antibody (Ab) were examined in murine adriamycin nephropathy (AN). BALB/c mice were divided into three groups: (a) normal mice, (b) adriamycin (ADR) with control immunoglobulin (Ig)G (ADR-IgG), and (c) ADR with anti-PD-1 Ab (ADR-Ab). AN was induced by a single intravenous injection of ADR. Anti-PD-1 Ab was given by intraperitoneal injection on alternate days from day 0 to day 10, or to day 18. Animals were killed at week 4. Renal function, histological change, and cytokine expression were examined. PD-1 mRNA was detected in kidney tissue of mice with AN in a dose- and time-dependent manner. PD-1 was mainly expressed on injured tubule cells and some interstitial cells, which co-stained with alpha-smooth muscle actin in AN, but not in normal kidney. Anti-PD-1 treatment up to day 18, but not to day 10, worsened glomerular and tubulointerstitial injury. The ratio of urinary protein/creatinine was significantly higher in ADR-Ab mice than ADR-IgG mice. The number of macrophages was significantly increased in ADR-Ab mice compared with ADR-IgG mice. Blockade of PD-1 worsened progressive renal histopathological and functional injury in murine AN. This suggests a possible protective role for PD-1 in chronic renal disease, and its potential as a treatment to slow disease progression.