5.1 defence mechanisms

Question 1

What is a general defence?

Answer 1

Immediate defences which are the same for all pathogens.

EG: The skin, phagocytosis

Question 2

What is a specific defence?

Answer 2

Less rapid, but long lasting defences, carries out by lymphocytes, as either;

• cell mediated responses by T lymphocytes
• humoral defences by B lymphocytes

Question 3

How do lymphocytes recognise non-self cells?

Answer 3

• Each type of cell has specific receptors on their surface.
• the variety of 3 D structure of surface proteins distinguishes one cell from another, and allow self cells to identify pathogens, non-self material, toxins and abnormal body cells.
• however this may cause them to reject transplant tissues

Question 4

How do lymphocytes recognise self cells?

Answer 4

• each type of lymphocyte is capable of recognising a different chemical shape.
• in a fetus, they are constantly colliding almost exclusively with self cells
• some lymphocytes will have receptors which fit own cells
• these either die or are suppressed.
• the remaining lymphocyte will fit non self material
• in adults, this occurs in the bone marrow, and any lymphocytes which show an immune response undergo programmed cell death.

Question 5

What are lymphocytes?

Answer 5

• types of white blood cell
• produced by stem cells in the bone marrow
• involved in specific responses
  2 types of lymphocytes:
  B Lymphocytes- Mature in the bone marrow, involved in humoral immunity.
  T lymphocytes- Mature in the thymus gland, involved in cell-mediated immunity