Innate Immunity

Innate immunity is an old system that is seen in all members of the animal kingdom including invertebrates. Examples of innate immunity include the skin and mucous membranes. Unlike adaptive immunity, innate immunity lacks specificity.

Anatomic Barriers to Pathogens: In addition to cellular and humoral immune responses, anatomic barriers such as the skin and membranes also provide protection from pathogens. The skin, for example, contains an outer layer called the epidermis, which is packed with epithelial cells. The outer layer of cells is dead and filled with a protein called keratin. Beneath the epidermis is a thicker layer called the dermis which is composed of connective tissue and contains blood vessels, hair follicles, sebaaceous glands and sweat glands. The dermis produces an oily secretion called sebum which maintain the ph of the skin between3-5. This acts as a physiologic barrier  which is inhibitory to the growth of most microorganisms.

Mucous membranes can be found in the respitory and urogenital tracts. In the lower respitory tract, the mucous membrane is covered by cilia, which propel mucus entrapped microorganisms from these tracts. Mucous secretions such as lysozme also acts as a physiological barrier to pathogens. This hydrolitc enzyme is able to cleave the peptidoglycan layer of bacterial cells walls. Mucous membranes are not fullproof, however. In fact, pathogens like the influenza virus (flu) has a surface molecule that enables it to attach to cells in the mucous membrane. Gonorrhea also has surface projections that allow it to bind to mucous membrane epithelia cells in the urogential tract..