C-X-C chemokine receptor type 4 (CXCR-4, CD184) is a receptor for the C-X-C chemokine CXCL12 (SDF-1) that transduces a signal by increasing intracellular calcium ions levels and enhancing MAPK1/MAPK3 activation. CD184 also acts as a receptor for extracellular ubiquitin. CD184 is involved in haemostasis, in cardiac ventricular septum formation and acts as a coreceptor with CD4 for HIV-1 isolates. Defects in CD184 are a cause of WHIM syndrome (warts, hypogammaglobulinemia, infections and myelokathexis).