What are first, second and third line of defense in our body against infections Name each group.

Dear Student,

1. The first line of defence against infectious diseases is the Physical and physiological barriers also sometimes called surface barriers, which includes:

• Skin : that protects external boundaries of the entire body.
• Mucous membranes: found in internal organs like gastrointestinal tract, respiratory tract etc. and helps to protect the internal boundaries of the entire body.
• Body secretions like sweat, sebum, tears, mucus, acid in the stomach etc.

2. The second line of defence are the non specific immune responses utilising cells of the immune system like macrophages, neutrophils, interferons, and complement proteins. They cause rise in body temperature, redness, inflammation etc. in response to infections. This line of defence cannot differentiate between pathogens and give same response for all infections.

3. The third line of defence includes the specific immune responses by Lymphocytes(B and T cells).

• B cells produce antibodies against specific antigens
• B cells also differentiate to form memory cells, which ensures long term safety from a particular antigen as the cells recognise them.
• T cells are of 3 types: T helper(helps B cell activation), T Cytotoxic(releases chemicals and effective specially against cancerous cells), T suppressor(blocks the actions of some other types of lymphocytes, to keep the immune system from becoming over-active).

The first and second line of defence are a part of innate immunity while third line of defence is adaptive.

Hope this helps.