However, monocytes from AA donors have limited extracellular receptor kinase (ERK) activation and no JNK, p38, or Smad2/3 activation, but significantly activate ERK in response to SDF-1, in contrast to high-level activation of these pathways without further SDF-1 induced enhancement in SSc patients [398]. Here, CXCL12 is linked to systemic sclerosis.