Surfactant protein A is opsonin in phagocytosis of herpes simplex virus type 1 by rat alveolar macrophages.
In the present study we used flow cytometry to investigate the phagocytosis of fluorescein isothiocyanate-labeled herpes simplex virus type 1 (FITC-HSV-1) by rat alveolar macrophages and the effects of surfactant protein A (SP-A) on this process. The phagocytosis of FITC-HSV-1 by alveolar macrophages, which was studied as a model for virus phagocytosis in general, was strongly enhanced in the presence of SP-A. The SP-A-mediated phagocytosis was time and concentration dependent, reaching a maximal level after 15 min of incubation and at an SP-A concentration of 5 micrograms/ml. Using a fluorescence quenching technique, we could show that at least 65% of the viruses were indeed internalized by the macrophages. The addition of SP-A to the system was sufficient for the phagocytosis of FITC-HSV-1 by the alveolar macrophages, suggesting that SP-A acts as an opsonin. This hypothesis was further strengthened by the observation that F(ab')2 fragments of immunoglobulin G directed against SP-A could abolish FITC-HSV-1 phagocytosis by alveolar macrophages preincubated with SP-A. Comparing the opsonic capacity of serum and SP-A, SP-A proved to be twice as potent as serum in stimulating phagocytosis of FITC-HSV-1 by alveolar macrophages. Complement factor C1q, which is known to possess a similar collagen-like domain as SP-A, did not stimulate phagocytosis of FITC-HSV-1 by alveolar macrophages nor did it inhibit SP-A-mediated HSV-1 phagocytosis. This study demonstrates that SP-A may play an important role in the antiviral defenses of the lung.
van Iwaarden
J F
JF
Laboratory of Veterinary Biochemistry, University of Utrecht, The Netherlands.
van Strijp
J A
JA
Ebskamp
M J
MJ
Welmers
A C
AC
Verhoef
J
J
van Golde
L M
LM
D000818:Animals; D000890:Anti-Infective Agents; D001790:Blood Physiological Phenomena; D015922:Complement C1q / Q000494:pharmacology; D016650:Fluorescein-5-isothiocyanate; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006801:Humans; D008264:Macrophages / Q000502:physiology*; D009895:Opsonin Proteins / Q000502:physiology*; D010587:Phagocytosis / Q000187:drug effects; D011510:Proteolipids / Q000502:physiology*; D011650:Pulmonary Alveoli / Q000166:cytology / Q000502:physiology*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000502:physiology*; D018139:Simplexvirus; D013861:Thiocyanates
D000890:Anti-Infective Agents; D005452:Fluoresceins; D005456:Fluorescent Dyes; D009895:Opsonin Proteins; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D013861:Thiocyanates; D015922:Complement C1q; D016650:Fluorescein-5-isothiocyanate