The prototypic tissue pentraxin PTX3, in contrast to the short pentraxin serum amyloid P, inhibits phagocytosis of late apoptotic neutrophils by macrophages.
OBJECTIVE
Phagocytosis of apoptotic cells can be facilitated by complement components and short pentraxins, such as serum amyloid P (SAP). In contrast, the long pentraxin PTX3 was shown to inhibit phagocytosis of apoptotic Jurkat cells by dendritic cells and to bind late apoptotic polymorphonuclear leukocytes (PMNs). Recently, levels of the pentraxin PTX3 were shown to parallel disease activity in small-vessel vasculitis, which is often characterized by leukocytoclasia, a persistence of leukocyte remnants in the vessel wall. We undertook this study to test our hypothesis that PTX3 inhibits phagocytosis of late apoptotic PMNs by macrophages, thereby leading to their accumulation in the vessel wall.


METHODS
Macrophages were allowed to phagocytose late apoptotic or secondary necrotic PMNs that were incubated with or without PTX3 for 30 minutes prior to phagocytosis. Phagocytosis was allowed to occur in the presence of 30% normal human serum with or without SAP and with or without depletion of complement. To discriminate between an inhibitory effect of PTX3 on binding and the internalization of apoptotic PMNs into macrophages, internalization was blocked by cytochalasin B.


RESULTS
SAP and complement were both necessary for effective in vitro phagocytosis. In contrast, PTX3 inhibited phagocytosis in a dose-dependent manner, from 11% inhibition at 6.25 microg/ml to almost complete inhibition at 100 microg/ml. Furthermore, PTX3 partly affected binding of apoptotic PMNs to macrophages.


CONCLUSIONS
PTX3, in contrast to SAP and complement, inhibits phagocytosis of late apoptotic PMNs by monocyte-derived macrophages in a dose-dependent manner. Therefore, PTX3 can play a role in the development of leukocytoclasia by affecting the clearance of apoptotic PMNs, thereby inducing their accumulation in the vessel wall.
van Rossum
André P
AP
University Hospital Groningen, Groningen, The Netherlands.
Fazzini
Fausto
F
Limburg
Pieter C
PC
Manfredi
Angelo A
AA
Rovere-Querini
Patrizia
P
Mantovani
Alberto
A
Kallenberg
Cees G M
CG
D017209:Apoptosis / Q000502:physiology*; D002097:C-Reactive Protein / Q000502:physiology*; D002478:Cells, Cultured; D003571:Cytochalasin B / Q000494:pharmacology; D006801:Humans; D019169:Jurkat Cells; D008264:Macrophages / Q000502:physiology*; D009504:Neutrophils / Q000502:physiology*; D010587:Phagocytosis / Q000502:physiology*; D000683:Serum Amyloid P-Component / Q000502:physiology*; D000099153:Pentraxins
D002097:C-Reactive Protein; D003571:Cytochalasin B; D000683:Serum Amyloid P-Component; D000099153:Pentraxins