They are released from triglycerides by lipolysis. The mucus is mixed with secretory IgA secreted by local plasma cells. The IgA is triggered into production during the first microbial attack, but on all subsequent attacks by the same organism, it is produced faster and in much greater quantities than the first time. That enables it to cover the surface of the invading organism and so to prevent it from adhering to the underlying epithelium. Barrier Support in the Skin A. Fatty acids from the sebaceous glands lower the skin pH to around 5.5, too low for a great many bacteria to survive.
Fungi do fairly well at that pH, however.
B. Some of the fatty acids exert their own particular antimicrobial effect as well. C. Mammary glands can be thought of as specialized skin glands, and they are already known to secrete the antimicrobial compounds lysozyme, lactoferrin, and lactoperoxidase. Saliva flushes the mouth and esophagus with each swallow, and is replenished from the salivary glands. Calprotectin is added to the saliva by keratinocytes in the mouth. Whether this is also true of the other squamous mucosae is not known.