CCL24 binds exclusively to the CCR3 receptor. CCL24 activates some of the immune/inflammation pathways that ligands for CCR5 activate but not as broadly. By targeting CCL24 rather than CCR3 they're missing out on the negative effects of the other ligands that bind to CCR3. CCR3 binds CCL-5 (RANTES), CCL-7, CCL-8, CCL11, CCL24, CCL26 and MCP-4. In common CCR5 binds CCL5, CCL7, CCL8 and CCL11. CCR3 binding affinity is much less with CCR5, unsure about the others. Given the higher rate of expression of CCR5 than CCR3, CCR5 would be the better target.