When co-cultured with HIV-1 infected mononuclear cells and human glial cells (astrocytoma, glial and primary human astrocyte), tumour necrosis factor alpha (TNF-α) and interleukin-1β are produced, and large amounts of LTB4, LTD4, LXA4, and PAF, were also found in media from this co-culture (Fig. 4) (Genis et al. 1992). So far, this is the only in vitro study to prove, that LXs are produced in direct response to viral infection. However, the role of LXs in this infection model has not been investigated. Synthetic peptides derived from human immunodeficiency virus type 1 gp120 activate the 7-transmembrane GPCR FPR2/ALX, down-regulating the expression and function of chemokine receptors CCR5 and CXCR4 in monocytes (Deng et al. 1999).