What is the difference between the primary and secondary immune response?

The Primary Immune Response occurs at first contact with the pathogen. 

The body takes several days to build up a sufficient amount of antibodies. There is a three-pronged attack in response to primary exposure to infection, which is non specific and is often referred to as the second line of defense. It involves: 

1. Inflammation - macrophages and other white blood cells release alarm chemicals, including histamine which makes capillaries more leaky. This causes leucocytes (white blood cells to move into the area. 

2.Phagocytosis- phagocytes (neutrophils and leucocytes will engulf some of the invading pathogen when they recognise the presented foreign antigen.

3. Interferon- Macrophages will produces chemicals that inhibit the proliferation of the pathogen cells. 

(All of the above is a non-specific response, which happens due to recognising universal proteins and glycoproteins that are present in many bacterial and viral strains).

The Specific, but still innate/primary response happens next. 

1.T lymphocytes and B lymphocytes are made in the bone marrow. T cells migrate to the thymus, and B cells mature in the bone marrow. The T cells are involved in the cell mediated response where upon antigen presentation, they mount an attack on the pathogen dependending on whether they are a T killer, memory, helper or suppressor cell. B cells proliferate and these clones turn into plasma cells which make antibodies or memory cells.

 

The secondary immune response 

Should the body encounter an antigen it has responded to in the past, T memory cells and plasma cells are already able to deal with it efficiently (hence the term, adaptive immunity ).Plasma cells which are waiting in the lymph nodes quickly proliferate  and the anti body level rises in response to a secondary attack.