As aforementioned, CCL3 and CCL4 are two structurally and functionally related CC chemokines. CCL3 and CCL4 were both discovered in 1988, when Wolpe et al. purified a protein doublet from the supernatant of lipopolysaccharide (LPS)-stimulated murine macrophages [57]. Because of its inflammatory properties in vitro as well as in vivo, the protein mixture was called macrophage inflammatory protein-1 (MIP-1). Further biochemical separation and characterization of the protein doublet yielded

two distinct, but highly related proteins, MIP-1α and MIP-1β[58]. From 1988 to LY294002 supplier 1991, several groups reported independently the isolation of the human homologues of MIP-1α and MIP-1β[59–61]. As Cobimetinib a consequence, alternate designations were used for MIP-1α (LD78α, AT464·1, GOS19-1) and MIP-1β (ACT-2, AT744·1), similar to other members of chemokine superfamily. In an attempt to clarify the confusing nomenclature associated with chemokines and their receptors, a new nomenclature was introduced by Zlotnik and Yoshie in 2000 [37]. MIP-1α and MIP-1β were renamed as CCL3 and CCL4. The non-allelic

copies of CCL3 and CCL4 were designated as CCL3L (previously LD78β, AT 464·2, GOS19-2) and CCL4L (previously LAG-1, AT744·2). CCL3 and CCL4 precursors and mature proteins share 58% and 68% identical amino acids, respectively (Fig. 2). Both chemokines are expressed upon stimulation by monocytes/macrophages, T and B lymphocytes and dendritic cells (although they are inducible in most mature haematopoietic cells). Functionally, CCL3 and CCL4 are potent chemoattractants of monocytes, T lymphocytes, dendritic cells and natural killer cells [47]. Despite these similarities, CCL3 and CCL4 differ in the recruitment of specific T cell subsets: CCL3 preferentially very attracts CD8 T cells

while CCL4 preferentially attracts CD4 T cells [62]. Interestingly, Bystry and co-workers demonstrated that B cells and professional antigen-presenting cells (APCs) recruit CD4+CD25+ regulatory T cells via CCL4 [63]. This role of CCL4 in immune regulation was reinforced later by Joosten et al. [64], who identified a human CD8+ regulatory T cell subset that mediates suppression through CCL4 but not CCL3. CCL3 and CCL4 also differ in their effect on stem cell proliferation: CCL3 suppresses proliferation of haematopoietic progenitor cells [65]. CCL4 has no suppressive or enhancing activity on stem cells or early myeloid progenitor cells by itself, but has the capacity to block the suppressive actions of CCL3 [66]. A different receptor usage may help to explain, at least in part, why these molecules have overlapping, but not identical, bioactivity profiles: CCL3 signals through the chemokine receptors CCR1 and CCR5.