Question

Identify at least four mechanisms by which a healthy host resists infection.

Answer 1

The mechanisms by which a healthy host resist infection are:-

1. Surface barriers- They protect from infection including mechanical, chemical and biological barriers. They form first line of defence against infection. Skin of animals, waxy cuticle of leaves are examples of mechanical barriers. The mucous secretions of skin, respiratory tract entraps and kills pathogen, hence form chemical barriers.

2. Inflammation- It is the first response of immune system to infection. It includes redness, swelling, pain caused by injured or infected cells. They produce prostaglandins that produce fever. These promote healing of damaged tissue following removal of pathogen.

3. Cellular barriers- Leukocytes such as macrophages, neutrophils, dendritic cells, natural killer cells. They identify and eliminate pathogens either by attacking them or engulfing and killing them. Phagocytosis is an important feature of cellular barriers.

4. Complement system- The complement system is a biochemical cascade that attacks the surface of foreign cells. This response is activated by complement binding to antibodies that have attached to pathogens or by binding to carbohydrates on their surface. This activates their proteases activit resulting in killing of pathogens by disrupting their plasma membrane.