In Vitro Control of Neutrophilic Phagocytosis of IgG-Coated SRBC by Macromolecules Involved in Released Products From Platelets

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Abstract
Analysis of macromolecular fraction of platelet release products (PRPr) was undertaken after we observed that pretreatment of human neutrophils with macromolecules (>105 daltons) involved in PRPr enhanced phagocytosis of IgG-sensitized sheep red blood cells (IgG-SRBC). Sephadex G-200 gel filtration of PRPr revealed two macromolecular activators and two suppressors of neutrophilic phagocytosis of IgG-SRBC: MAPP(s), macromolecular activator(s) of phagocytosis from platelets; MSPP(s) macromolecular suppressor(s) of phagocytosis from platelets. The estimated molecular weights of the respective MAPPs were 100 kdaltons to 140 kdaltons (kd) (s-MAPP) and 200 kd to 290 kd (I-MAPP) and those of the respective MSPPs were 60 kd to 100 kd (s-MSPP) and 400 kd to 500 kd (I-MSPP). It is suggested that an l-MAPP molecule has at least an s-MAPP molecule as a functional unit and that MAPPs and larger MSPP (I-MSPP) might be glycoproteins, while smaller MSPP (s-MSPP) seems to contain neither carbohydrates nor lipids. As far as the effects of serum and plasma on phagocytosis of IgG-SRBC by neutrophils are concerned, the serum gave twice as much phagocytic activity as the plasma. Substantial MAPP-like activities were observed In the serum and MSPP-like activities were observed in both the serum and plasma.