Autacoid properties of lysophosphatidylserine.

The hypothesis of this study is summarized in Fig. 6. Phosphatidylserine due to distribution in the internal side of plasma membrane is prevented to react with the extracellular environment. When injury to cell occurs, phospholipid asymmetry is lost and the exposed phosphatidylserine becomes a signal of cell damage. Phosphatidylserine may activate defense reactions while it is still anchored to plasma membrane (Zwaal, 1978; Tanaka and Schroit, 1983). Alternatively, the soluble lysophosphatidylserine is generated, ready to diffuse and transmit the information of tissue damage to other cells. In this sequence of events, lysophosphatidylserine becomes an autacoid, originated from a membrane phospholipid. In rodents, lysophosphatidylserine seems specifically devoted to activate mast cells. The role of these cells in the regulation of the immune reactions and in tissue repair has been advocated (Dexter et al., 1981). The lysophosphatidylserine-induced mast cell activation has been shown in vivo and in vitro in a variety of rodent species (mouse, rat, gerbil, hamster). It may occur through a direct effect or through the participation of synergistic endogenous compounds. Structure-activity relationships in the action of lysophosphatidylserine show that the effect on mast cells is linked to a definite molecular organization. Determinants of the mast cell activation are the free amino group and the carboxyl group of the serine. Support to the general hypothesis of this study originates from the observation that active lysophosphatidylserine is generated within a population of leukocytes, the cells migrating in areas of wounded tissue (Mietto et al., 1987). Production of lysophosphatidylserine can be anticipated in pathological situations associated with extensive cell death (tumor growth, graft rejection, burns). At present, the observations on lysophosphatidylserine are confined to rodent mast cells. Other histamine-secreting cells (e.g., the human basophil) are unresponsive to this phospholipid (Kolster et al., 1987). Among the endogenous compounds interacting with lysophosphatidylserine, nerve growth factor seems of particular interest (Bruni et al., 1982). The synergism with lysophosphatidylserine has been confirmed in other laboratories (Sugiyama et al., 1985; Pearce and Thompson, 1986; Mazurek et al., 1986). The concerted effects by these two compounds on mast cells is in line with current opinion on the participation of nerve growth factor in the regulation of inflammatory and immune reactions (Mietto et al., 1987; Weskamp and Otten, 1987).(ABSTRACT TRUNCATED AT 400 WORDS)