In order to establish the genetic basis of these differences, we prepared F2 hybrids between BALB/c and CcS-16, infected them with L. tropica and measured their skin lesions, splenomegaly, hepatomegaly, parasite numbers in spleen, liver and inguinal lymph nodes, and serum level of CCL3, CCL5 and CCL7 during the transient early peak. This evidence concerns the gene CCL5 and Splenomegaly.