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Cystatins in human tear fluid
T Barka1, P A Asbell, H van der Noen
1Department of Cell Biology and Anatomy, Mount Sinai School of Medicine, New York, NY 10029.
Current Eye Research
|January 1, 1991
Summary
Tears contain significant levels of cystatins, which are inhibitory proteins that regulate cysteine proteinases. These findings highlight the presence and activity of cystatins in ocular fluids.
Area of Science:
- Biochemistry
- Ophthalmology
- Immunology
Background:
- Cysteine proteinases, including lysosomal cathepsins, are regulated by cystatins.
- Cystatins are found intracellularly and in extracellular fluids like tears.
- Tears play a role in ocular health and defense mechanisms.
Purpose of the Study:
- To quantify the apparent free cystatin activity in human tears.
- To determine the concentration of cystatins in tear fluid.
- To identify cystatin proteins present in tears using immunochemical methods.
Main Methods:
- Tears collected using Schirmer paper strips and capillary tubes from healthy volunteers.
- Cystatin activity determined by titrating with papain.
- Cystatin concentrations measured by indirect enzyme-linked immunosorbent assay (ELISA).
- Immunoblots used to detect and characterize cystatin proteins based on molecular weight and antibody reactivity.
Main Results:
- High apparent free cystatin activity detected in tears (28.8 ± 3.47 pmols papain inhibited/mg tear protein).
- Tears contain substantial cystatin-like immunoreactive material, approximately 10% of total tear proteins.
- ELISA revealed high cystatin S levels (94.7–115.5 µg/mg protein).
- Immunoblots identified a ~14 kDa protein reactive with anti-cystatin SN antibodies, and similar proteins with anti-cystatin S and C antibodies.
Conclusions:
- Human tears possess significant free cystatin activity and high concentrations of cystatins.
- Cystatins S, C, and SN are present in tear fluid.
- These findings suggest a role for cystatins in the innate immunity and homeostasis of the ocular surface.