Table 1.
Characteristics and functions of common HDPs at the ocular surface (OS).
| Type | Source | Functions |
|---|---|---|
| Lysozyme | - Tear fluid (secreted by tubuloacinar cells of lacrimal glands) - Corneal epithelium - Meibomian glands |
- Antimicrobial property (via hydrolysis and pore formation of cell wall) (20, 26) - Immunomodulatory function via interaction with various pattern recognition receptors (26, 27) |
| Lactoferrin | - Tear fluid (secreted by acinar cells of lacrimal glands) - Conjunctival epithelium - Corneal epithelium - Meibomian glands |
- Antimicrobial activity (via binding to free iron and membrane permeabilization) (28–30) and anti-biofilm (31) - Immunomodulatory function (anti- and pro-inflammatory) (32, 33) - Antioxidant (via inhibition of iron-dependent formation of hydroxyl radicals) (34) - Wound healing (32, 33) |
| Human alpha-defensins (or HNP)-1 to−4 | - Azurophil granules of neutrophils | - All: antimicrobial activity (via membrane perturbation) (35) - HNP-1 to−3: immunomodulatory (Pro-inflammatory and anti-inflammatory) (36–38) - HNP-1 to−3: anti-cancer (39, 40) |
| Human beta-defensins (HBD)-1 to−3 | - Conjunctival and corneal epithelium | - All: antimicrobial activity (via membrane perturbation) (41, 42) - All: immunomodulatory function (pro-inflammatory and anti-inflammatory) (42, 43) - HBD-3: wound healing (44) - All: anti-cancer (45, 46) |
| Cathelicidin | - Conjunctival epithelium - Corneal epithelium |
- Antimicrobial activity (via membrane perturbation) (47–52) and anti-biofilm (47, 53) - Immunomodulatory function (pro-inflammatory and anti-inflammatory) (54, 55) - Wound healing (48, 56) - Anti-cancer (40, 57) |
| Ribonucleases- (RNases) | - RNase-5: Tear fluid and corneal endothelium - RNase-7: Corneal epithelium and stroma |
- Antimicrobial activity (via binding to bacterial membrane lipoprotein and membrane perturbation) (58–66) - Immunomodulatory function (activates adaptive immunity) (67, 68) - Angiogenic and neurogenic (69, 70) - Wound healing (71) |
| Psoriasin | - Conjunctiva - Cornea - Lacrimal gland - Nasolacrimal duct |
- Antimicrobial activity (via zinc-dependent mechanism) (72, 73) - Immunomodulatory function (chemotaxis, activates adaptive immune system via CD4+) (74, 75) |
| Dermcidin | - Corneal epithelium - Tear fluid |
- Antimicrobial activity (via zinc-dependent mechanism) (76) |
| Histatin | - Tear fluid | - Antimicrobial activity (via membrane perturbation) (77, 78) - Anti-inflammatory function (79) - Wound healing property (80, 81) |
HNP, human neutrophil peptide/human alpha-defensin; HBD, human beta-defensins.