# A165 IL-6 ENHANCES THE ANTI-COLITIC THERAPEUTIC POTENTIAL OF HUMAN IL-4 POLARIZED MACROPHAGES

## TL;DR

This study shows that adding IL-6 to IL-4-polarized human macrophages improves their ability to reduce colitis in mice, challenging the idea that IL-6 is purely harmful.

## Contribution

The novel finding is that IL-6 enhances the therapeutic potential of IL-4-polarized macrophages in treating colitis.

## Key findings

- IL-6 does not disrupt the anti-inflammatory phenotype of IL-4-polarized macrophages.
- Macrophages treated with both IL-4 and IL-6 show better protection against colitis in mice.
- IL-6 reduces cell death in macrophages under oxidative stress, especially in those from Crohn’s disease patients.

## Abstract

Inflammatory bowel disease (IBD) is a group of inflammatory disorders, including Crohn’s disease and ulcerative colitis, that affect the gastrointestinal tract and can significantly impact patients’ quality of life. Forty percent of individuals with IBD are unresponsive to current therapies and a cure remains elusive. Macrophages play key roles in inflammation and tissue repair, with IL-4 treated macrophages, M(IL4)s, exerting an anti-inflammatory effect. We showed that systemic administration of human M(IL4)s reduced disease severity in murine colitis. Interleukin-6 is considered a pro-inflammatory cytokine, the levels of which are increased in IBD gut tissue. Murine studies suggest IL-6 may reinforce an M(IL4) phenotype, raising the possibility, and perhaps challenging dogma, that IL-6 could promote the beneficial effects of M(IL4)s. Therefore, I hypothesize that local tissue signal IL-6 enhances the anti-inflammatory properties of human M(IL4)s.

1. Determine the effect of IL-6 on the phenotype of human M(IL4)s.

2. Determine the effect of IL-6 on M(IL4) function, assessing (a) wound healing capacity and (b) cell death.

3. Compare the efficacy of M(IL4) and M(IL4+IL6) in the DNBS-rag1-/- mouse colitis.

M(IL4)s were differentiated from blood monocytes from male and female healthy volunteers and individuals with Crohn’s disease. M(IL4)s ± IL-6 (10 ng/mL; 24h) were assessed for (1) phenotype (mRNA expression) and (2) function. Function was evaluated through testing (a) conditioned medium from M(IL4+IL6)s in an in vitro Caco2 epithelial scratch-wound assay and (b) viability in response to hydrogen peroxide (H2O2) (oxidative stress) via LDH release. (3) M(IL4)s or M(IL4+IL6)s were delivered intraperitoneally (106 cells) and 48h later, rag1-/- mice received 5mg intra-rectal DNBS. Colitis was assessed 72h later. Non-treated M(0) and M(IL6) serve as controls.

M(IL4)s and M(IL4+IL6)s show similar increased expression of CD206 and CCL18, and decreased CD14 mRNA (n=6-7). Conditioned media from both M(IL4)s and M(IL4+IL6)s promoted a similar degree of epithelial migration in the wound healing assay (n=5). Macrophages from patients had increased susceptibility to H2O2-induced death, which was reduced in the M(IL4+IL6) group (n=6 healthy donors; n=6 Crohn’s). M(IL4+IL6)s were more effective than M(IL4)s in protecting against murine colitis as determined by body weight, colon length and a macroscopic disease score (n=8 mice, 3 exps.).

IL-6 does not abrogate the M(IL4) phenotype or wound healing capacity and protects the cell from H2O2-induced cytotoxicity. Also, M(IL4+IL6)s have a superior anti-colitic effect when compared to M(IL4)s from the same donor. The data support macrophage transfer to treat colitis and indicate that an element of an inflamed environment can enhance the anti-colitic effect of human M(IL4)s.

CIHRCartier Family Student Research Award in Gastroenterology and Hepatology, Alberta Graduate Excellence Scholarship, Helmsley Grant