CXCL12 (also known as stromal cell-derived factor 1 or SDF-1) and its receptor CXCR4 are not part of the six major cytokine families. Regarding the activation of CXCL12 cytokine secretion, several cell types can be involved, including: 1) Stromal cells: CXCL12 is originally derived from stromal cells and is present in the extracellular matrix. 2) Fibroblasts: These cells can produce CXCL12 and contribute to its secretion. 3) Endothelial cells: Endothelial cells, which line the blood vessels, can also produce and secrete CXCL12. 4) Immune cells: Different immune cell types, such as macrophages, monocytes, and T cells, are known to secrete CXCL12. As for the target cells with CXCR4 receptors, CXCL12 binds to CXCR4, triggering various cellular responses. Some of the cell types expressing CXCR4 and thus responding to CXCL12 signaling include: 1) Leukocytes: CXCR4 is expressed on various leukocytes, such as T cells, B cells, monocytes, and neutrophils. 2) Cardiomyocytes: CXCR4 is found on cardiomyocytes, the cells that make up the heart muscle. 3) Fibroblasts: Fibroblasts, which play a crucial role in tissue remodeling and repair, also express CXCR4. 4) Endothelial cells: Endothelial cells themselves can express CXCR4 and respond to CXCL12 signaling.

Apparently its the book called Kuby

Janeway's Immunobiology