Cytokine milieu in human sera seems to have a pro-osteoclatogenic effect regardless of its origin with respect to healthy condition. However, inflammatory factors present in the sera of SpA patients enhance the osteoclastogenic potential of PBM, as documented especially in AS sera presenting with significant, 7fold increased serum CRP levels (P = 0.003), and thus may contribute to aggravation of the osteoporotic condition of SpA patients.