Specific Immune Response

Hiya,

Specific immunity allows for a targeted response against a specific pathogens. The immune system has several specialised cells which work together in a specific immune response against pathogens;

  Microscopic image of blood(Joe Filipe, Unsplash)

• Macrophages are large white blood cells (WBC) that help in immune response by engulfing pathogens using endocytosis and partially digesting them by creating a phagosome (using lysosomes). Macrophages then use a special protein complex to present the antigen marker of the pathogen on its exterior. It does this to increase the likelihood of the pathogen's antigen marker colliding with a B or T lymphocyte to initiate immune response. They are found in the lymphatic system and lymph nodes as monocytes where they differentiate into macrophages.

• T lymphocytes (or T cells) are large WBC that have specialised receptors that can detect the antigen markers on pathogens or the antigen-presenting macrophages. T cells can come in three main forms; 
• T-helper cells; release cytokines to stimulate phagocytosis and development of B lymphocytes
• T- memory cells; provide long term immunity
• T-killer cells; attacks or kills pathogens of host cells, the antigens must be complimentary
• T cells are produced in the thymus ( a lymph node between the lungs)

• B lymphocytes are similar to T lymphocytes but come in two forms; as B memory cells ( to provide long term immunity) or can differentiate into plasma cells to make and release antibodies.

Because each pathogen has specific antigen markers, specific lymphocytes must be used to break them down and produce the required antibodies. Clonal selection is the activation of specific T and B cells when they come into contact with a pathogen's antigen. As an organism enters the body, clonal selection must occur to identify the specific T or B cell to be used and this cell will replicate to combat the organism.

When pathogens infect host cells, some of the pathogen attaches to the plasma membrane of the host cell; this acts as a distress for the immune system and marks the host cell as infected and should be destroyed.

As well as presenting antigen markers from pathogens, macrophages release monokines which attract neutrophils to the area where the macrophage picked up the pathogen. Attraction towards a chemical is called chemotaxis.

T-lymphocytes regulate the growth and differentiation of T cells and certain B cells through the release of secreted proteins called interleukins. These interleukines trigger clonal expansion. Clonal expansion is where T and B cells divide by expansion to produce large quatities of clones, which can differentiate into subtypes.

Interleukines and monokines are types of cytokine; cytokines are chemicals used in cell signalling to trigger a response in another cell. 

On the other hand, chemicals called interferons can inhibit instead of trigger replication; for example they can inhibit viral replication and stimulate T killer cells.

We can use interferons in cancer treatment to prevent the cancerous cells from growing and replicating and encouraging T killer cells to destroy these cancerous cells.