In the striatum, we also see clustering within the fentanyl-treated groups based on infection status: EcoHIV-infected mice treated with fentanyl had higher concentrations of CCL2, CCL4, CCL5, and CCL11 but lower levels of CCL3 and CXCL10 than the uninfected, fentanyl-treated animals. The gene discussed is CXCL10; the disease is infection.