CCL18
Description
The CCL18 (C-C motif chemokine ligand 18) is a protein-coding gene located on chromosome 17.
CCL18 is a small cytokine belonging to the CC chemokine family. Its functions have been extensively studied in laboratory settings, but characterizing its physiological effects in living organisms has been challenging due to the lack of a similar protein in rodents for study. The identification of CCL18's receptor in humans only recently has provided scientists with a valuable tool for understanding its role in the body.
CCL18 is mainly produced and secreted by the innate immune system, primarily affecting the adaptive immune system. It was previously known as Pulmonary and activation-regulated chemokine (PARC), dendritic cell (DC)-chemokine 1 (DC-CK1), alternative macrophage activation-associated CC chemokine-1 (AMAC-1), and macrophage inflammatory protein-4 (MIP-4).
The CCL18 gene shares the most similarity with CCL3. It is located on chromosome 17, alongside numerous other macrophage inflammatory proteins (MIPs). The gene itself comprises 3 exons and 2 introns. However, unlike other chemokines, CCL18 incorporates 2 pseudo-exons (exons that are not present in the final peptide) within the first intron. These pseudo-exons suggest that CCL18 originated through a gene fusion event between CCL3-like protein encoding genes, and over time has accumulated mutations that have led to its distinct function. CCL18 is an 89 amino-acid-long protein, with a 20 amino-acid-long peptide signaling sequence (for signaling its secretion) at the N’ terminus, which is cleaved in the endoplasmic reticulum, resulting in a 69 amino-acid-long mature protein.
CCL18 is a chemotactic factor that attracts lymphocytes but not monocytes or granulocytes. It may play a role in B-cell migration into B-cell follicles in lymph nodes. CCL18 attracts naive T-lymphocytes towards dendritic cells and activated macrophages in lymph nodes, exhibiting chemotactic activity for naive T-cells, CD4+ and CD8+ T-cells, suggesting a role in both humoral and cell-mediated immunity responses.
CCL18 is also known as AMAC-1, AMAC1, CKb7, DC-CK1, DCCK1, MIP-4, PARC, SCYA18.
