The human antimicrobial peptide hCAP18 in epithelial defense

Abstract

Gene-encoded antimicrobial peptides serve a protective role in host defense. They are multifunctional effector molecules in innate immunity - the nonadaptive immune system -with the capacity to kill a broad spectrum of microorganisms. In contrast to adaptive immunity, which is highly specific, the innate immune system provides a rapid and nonspecific response, thereby contributing to the first line of defense. Cathelecidins constitute a family of antibacterial peptides. hCAP1 8, the precursor of the LL-37 antimicrobial peptide, is the only cathelecidin in humans while there are several in other species.

We first analyzed fluid from wounds with different etiology for antibacterial and biochemical factors. We showed that wound fluid can be analyzed reproducibly and characterized biochemically. Separation and identification of such fluids yielded peptide components likely to reflect necrosis and to function as antibacterial and possible wound healing factors (Paper 1).

We studied the role of hCAP1 8 in normal wound healing and in chronic non-healing ulcers. Using skin biopsies from healthy volunteers and from patients, we determined the level and expression pattern of hCAP1 8. Our results demonstrate the presence of hCAP1 8 in both types of wounds. Maximal levels of hCAP 18 were attained at 12h-2days post-wounding in surgical wounds. Total hCAP 18 protein levels in the chronic ulcers were below 20% of the maxima detected in the surgical wounds. Processed active LL-37 peptide was demonstrated in normal wound healing but was barely detectable in the chronic ulcers (Paper 2).

In addition to providing a mechanical barrier between the body and the environment epithelia function as an immunological organ. Investigating the expression of hCAP 18 in inflammatory skin disorders we found up- regulation of the hCAP 18 gene in the keratinocytes of inflammatory dermatoses such as lesional psoriasis, nickel allergy and atopic dermatitis, but not in normal quiescent epidermis (Paper3).

Further investigation of hCAP1 8 in squamous epithelia demonstrated that hCAP1 8 was constantly expressed at both RNA and protein levels in epithelia of tongue, esophagus, cervix and vagina. Expression of IL- 6 co-localized with hCAP 18 in these tissues. The hCAP 18 gene contains promotor elements that are potentially regulated by IL-6, and our findings suggest a potential local mechanism for the up-regulation of hCAP 18 on epithelial surfaces (Paper 4).

To assess the potential role of hCAP 18 in tumor host defense, we investigated its expression in human breast cancer of varying types and malignancy. hCAP 18 was strongly up-regulated in the tumor cells compared to the low constitutive expression in normal benign mammary epithelia. Further, the highest levels of hCAP 18 protein were detected in the most malignant tumors, and immunoblotting revealed processed active LL-37 only in these tumors. Thus our results do not support a protective role for hCAP 18 in tumor host defense, but rather suggest that hCAP 18 may provide a survival advantage for the tumor (Paper 5). In summary our studies reveal a role for the innate immunity effector hCAP 18 in epithelial defense.