Monocytes in the rat

We review our methods for definition and phenotypical characterisation of n ormal and activated rat monocytes. To obtain a comprehensive sample of all blood monocytes including cells from the marginal pool of the blood stream, we extensively perfuse the extrapulmonary circulation with cold PBS/EDTA. Normal rat monocytes are isolated from untreated specified pathogen-free ma le LEW rats. In vivo activated monocytes are investigated after three days of infusion of recombinant IFN-gamma or during acute renal allograft reject ion. Rat monocytes are defined by reactivity with mAbs ED1 and ED3, detecting a lysosomal membrane antigen and a member of the signal-regulatory protein fa mily resprecivel!; as well as by expression of CD11b. Concomitantly rat mon ocytes are characterized by the absence of CD5, the absence of the B cell f orm of CD45R, and the absence of reactivity with mAb RP-1. The majority of the monocytes from untreated LEW rats are CD4(+), CD11a(high), CD18(high), CD43(high), CD62-L-, CD161(-), and MHC class II-. Upon stimulation of the i mmune system in vivo, a second monocyte population increases in number. The se cells have a larger diameter and an increased granularity. They are CD4( -), CD11a(int), CD18(int), CD43(low), CD62(-)L(+), CD161(int), and MHC clas s II+. Although some reagents are not yet available (e.g. antibodies against rat C D14 and CD16), rat monocytes can be defined and their state of activation c an be characterized. The functionally important population of monocytes, wh ich have already marginated, is accessible by perfusion and relatively high monocyte numbers are isolated per rat. As specified pathogen-free rats are available and numerous experimental systems involving acute or chronic inf lammation have been established in rats, differentially activated monocytes may be investigated. The rat is thus a suitable experimental animal for ba sic research on monocytes.