C5AR1 and mastitis: Because LukMF′, LukED, HlgAB, and HlgCB specifically permeabilise cells carrying their designated target receptors, we were able to use the CCR1, CXCR2, and C5aR1 expressing cells to quantify the secretion of functional leukocidins into the culture supernatant of bovine mastitis isolates10.