Figure 4. Upon colitis induction, Trem1^−/− x Rag2^−/− mice exhibit substantially reduced inflammatory infiltrates and diminished expression of pro-inflammatory mediators.

(A–C) Lamina propria cells were isolated from the colon of Trem1^+/+ x Rag2^−/− and Trem1^−/− x Rag2^−/− mice 12–13 days post adoptive transfer of colitogenic CD4 T cells or from untransferred mice (healthy colons) and analysed by FACS. (A) After exclusion of doublets and dead cells, CD11b⁺ cells were discriminated from CD4⁺ T cells and further subgated into MHCII^lo Gr1⁺ (gate 1) and MHCII^hi Gr1⁻ (gate 2) cells. In gate 1, monocytes and neutrophils were identified according to their Ly6C^hi Gr1^int and Ly6C^int Gr1^hi phenotype, respectively. In gate 2, MHCII⁺ cells were further subdivided into two populations of MHCII^int Ly6C^hi and MHCII^hi Ly6C^lo cells. (B, C) Absolute numbers of total cells recovered from individual mice (symbols; lines indicate mean values per group) and mean values ± SEM for CD45⁺ cells, CD4⁺ T cells, CD11b⁺ cells and subsets defined within the CD11b⁺ gate as illustrated in (A). Per group, n = 9 mice adoptively transferred with CD4 T cells (B) and n = 4 untransferred (C) mice were analysed. (D) TREM-1 surface expression by neutrophils (Ly6C^int Gr1^hi), monocytes (Ly6C^hi Gr1^int) and CD11b⁺ Gr1⁻ Ly6C⁺ versus Ly6C⁻ subsets identified in the lamina propria (according to the gating strategy depicted in D) of colitic (n = 9) versus healthy (n = 4) Trem1^+/+ x Rag2^−/− mice. (E) Colonic tissues were assessed for the expression of pro-inflammatory mediators by qRT-PCR. Bars show mean values ± SEM for n = 9 mice. ***, p<0.001; **, p<0.01; *, p<0.05. N.D. = not determined due to insufficient cell numbers.