1.2.7.2 The humoral components of the skin's immun...
The humoral components of the skin's immune system include cytokines，immunoglobulins，complement，antimicrobial peptides，neuropeptides，etc.
Cytokines are a class of small-molecule soluble peptide mediators.A variety of cells in the epidermis can synthesize and secrete cytokines.Cytokines are divided into six categories：interleukin，interferon，hematopoietic clone stimulating factor，tumor necrosis factor，growth factor and transforming factor，and chemokine.Cytokines can act locally，or act systematically in a hormone-like manner.
Normal skin usually has no complement.The complement system is activated when the skin is inflamed.Complement can participate in natural immunity and acquired immunity by dissolving cells，immunoadsorption，sterilization，and allergic toxins and promoting the release of mediators.Complement deficiency is associated with certain skin diseases.For example，C1r，Cls，C2，and C4 deficiency are associated with systemic lupus erythematosus，lupus-like syndrome，and dermatomyositis；C1 inhibitor deficiency is associated with hereditary angioedema，SLE，and discoid to lupus erythematosus；C4 deficiency can increase the risk of vitiligo.(https://www.daowen.com)
Immunoglobulin refers to a globulin with antibody activity or chemical structure similar to that of an antibody and plays the role in acquired immunity.The content of immunoglobulin in normal skin is very low.Patients with certain autoimmune skin diseases（e.g.，lupus erythematosus，scleroderma，pemphigus，pemphigoid，and herpetic dermatitis）have significantly higher levels of autoantibodies.The latter forms immune complexes with corresponding autoantigens and deposits in the skin and other tissues and organs，leading to diseases.
There are more than 20 kinds of antimicrobial peptides，including antibacterial peptides，β-defensins，substance P，and chemokines.Antibacterial peptides are a kind of small molecule peptides that can directly kill a variety of pathogens and play an important role in normal skin innate immunity.Moreover，antibacterial peptides have chemotactic effects on neutrophils，macrophages，and T cells.In addition，skin nerve endings can release sensory neuropeptides such as calcitonin gene-related peptides，substance P，and neurokinase A after being stimulated by the external environment，causing chemotaxis to neutrophils and macrophages and resulting in local inflammation.