In the colon tissue of P. copri-colonized mice, genes involved in immune and inflammatory responses (e.g., Ccl2, Ccl24, Ccl3, Ccl4, Ccl7, Il1b, Il6ra, Ilf2, Tlr2, Tlr3, Tlr5, and six genes from the immunoglobulin superfamily), and genes involved in fat accumulation and obesity (such as Fabp2 and Ins2) had higher mRNA levels (Fig. 7c and Additional file2: Table S7). Here, CCL2 is linked to obesity due to melanocortin 4 receptor deficiency.