Members of the cathelicidin family of antimicrobial polypeptides are characterized by a highly conserved region (cathelin domain) and a highly variable cathelicidin peptide domain.

Cathelicidin peptides have been isolated from many different species of mammals. Cathelicidins were originally found in neutrophils but have since been found in many other cells including epithelial cells and macrophage

Macrophage

Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

s after activation by bacteria, viruses, fungi, or the hormone 1,25-D, which is the hormonally active form of vitamin D

Vitamin D

Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....

.

The cathelicidin family shares primary sequence homology with the cathepsin

Cathepsin

Cathepsins are proteases: proteins that break apart other proteins, found in many types of cells including those in all animals. There are approximately a dozen members of this family, which are distinguished by their structure, catalytic mechanism, and which proteins they cleave...

 family of cysteine proteinase inhibitors, although amino acid residues thought to be important in such protease inhibition are usually lacking. Cathelicidins serve a critical role in mammalian innate immune defense against invasive bacterial infection.

Family members

• Cathelicidin
• LL-37
• porcine PR-39
• human FALL-39
• hCAP-18
• CRAMP-1/2, Cathelin-related Antimicrobial Peptide

Clinical significance

Patients with rosacea

Rosacea

Rosacea is a chronic condition characterized by facial erythema . Pimples are sometimes included as part of the definition. Unless it affects the eyes, it is typically a harmless cosmetic condition...

 have elevated levels of cathelicidin and elevated levels of stratum corneum tryptic enzymes (SCTEs). Antibiotics have been used in the past to treat rosacea, but antibiotics may only work because they inhibit some SCTEs.

Higher levels of human cathelicidin antimicrobial protein (hCAP18), which are regulated by vitamin D

Vitamin D

Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....

, appear to significantly reduce the risk of death from infection in dialysis

Dialysis

In medicine, dialysis is a process for removing waste and excess water from the blood, and is primarily used to provide an artificial replacement for lost kidney function in people with renal failure...

patients. Patients with a high level of this protein were 3.7 times more likely to survive kidney dialysis for a year without a fatal infection.