Pulmonary surfactant protein A binds to Cryptococcus neoformans without promoting phagocytosis.
BACKGROUND
Evidence is accumulating that the alveolar collecting surfactant protein A (SP-A) plays an important role in the first line of defence against infiltrating pathogenic micro-organisms and viruses. The ability of SP-A to facilitate the binding and uptake of acapsular Cryptococcus neoformans by monocyte-derived macrophages, human alveolar macrophages, monocytes and polymorphonuclear leucocytes was investigated.


METHODS
Binding, competition and phagocytosis experiments were performed using a flow cytometry technique.


RESULTS
SP-A bound to both the acapsular and the encapsulated form of C. neoformans in a concentration-dependent manner. SP-A showed a threefold better binding to the acapsular yeast: this binding was partly calcium dependent and could be inhibited by mannose (ID50 = 3 mmol L-1) and glucose (ID50 = 2.1 mmol L-1) but not by galactose (ID50 = 391 mmol L-1). SP-A did not function as an opsonin in phagocytosis of acapsular C. neoformans for any of the phagocytes studied.


CONCLUSIONS
Our results indicate that SP-A binds in a concentration-dependent manner to both encapsulated and acapsular C. neoformans. Despite SP-A binding to the acapsular C. neoformans, phagocytosis by various phagocytes was not enhanced.
Walenkamp
A M
AM
University Hospital Utrecht, The Netherlands.
Verheul
A F
AF
Scharringa
J
J
Hoepelman
I M
IM
D000818:Animals; D001232:Aspergillus fumigatus; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D050260:Carbohydrate Metabolism; D003455:Cryptococcus neoformans / Q000378:metabolism*; D005690:Galactose / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D009980:Influenza A virus; D008358:Mannose / Q000494:pharmacology; D009895:Opsonin Proteins; D010586:Phagocytes; D010587:Phagocytosis; D011485:Protein Binding / Q000187:drug effects; D011510:Proteolipids / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000378:metabolism*; D051381:Rats
D006023:Glycoproteins; D009895:Opsonin Proteins; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D005947:Glucose; D008358:Mannose; D002118:Calcium; D005690:Galactose