Because CXCL12 is a potent chemotactic factor for T and pre-B lymphocytes [26, 27], plasma cells [28], and dendritic cells (DCs) [29] and expression of SDF-1 (CXCL12) receptor (CXCR4) is also documented on eosinophils [24, 30] and mast cells [31–33] - the two critical components in allergic conjunctivitis [33]. This evidence concerns the gene CXCR4 and atopic conjunctivitis.