Non Specific Defence Against Disease

Mammalian defence against infectious disease can be non-specific, otherwise known as innate, or specific (adaptive).

Non-specific defence can be further categorised into external (preventive) or internal (defensive). Physical barriers such as skin, mucous membranes and hair contribute to the body’s non-specific defence against disease. Commensal organisms on skin are also a physical barrier.
Chemical secretions such as lysosyme in tears, sebum on skin and stomach acid are also part of non-specific defence.
Nervous reflexes such as blinking, vomiting, coughing and sneezing are also defences against disease. Cilia which line the airways, as well as sweeping cells in the lungs and urinogenital tract, play a role in the non-specific defence.
Histamine is released from damaged/infected cells causing a localised increase in blood flow, increasing the movement of cellular response. Symptoms of the immunological response include redness of the infected area, fever and the area may appear red and swollen.
There are many types of cells which ingest invading microbes. Phagocytes are a form of white blood cell which engulf and destroy parasites in a vacuole through the process of phagocytosis. There are two kinds – macrophages and neutrophils. Macrophages are the largest phagocytic cell and are effective as well as long lived. Macrophages produce semi-liquid projections to capture microbes. Phagocytes use ‘debris’ from the parasite and display them as antigens on their surface (an example of interaction between specific and non-specific defence systems). White blood cells carry out ‘immune surveillance’. There are two forms of lymphocytes – T and B. T-lymphocytes are also known as natural killer cells and trigger apoptosis (programmed cell death) in abnormal cells. Apoptosis is triggered by cell death signals which activate inactive forms of DNAases and proteinases (caspases) which destroy the cell. Cell death signals may be extrinsic (triggered by