T lymphocytes

T lymphocytes

T lymphocytes

Lymphocytes are smaller than phagocytes and their nucleus fills most of the cell. They are produced before birth in the bone marrow.

T lymphocytes:

  • Migrate from bone marrow to the thymus (gland at base of breast bone) before they are mature. The thymus gland doubles in size between birth and puberty and then shrinks.
  • Have specific surface cell receptors (T cell receptors) which have similar structure to antibodies and are specific to one antigen.
  • T cells are activated when they meet an antigen in contact with host cell. This may be a macrophage with exposed antigen or a body cell that has been invaded by a pathogen and is displaying antigens on plasma membrane as a help signal.
  • Relevant T cells with matching receptors respond by dividing (mitosis).

There are three types of T cells:

Helper T cells:

  • Release cytokines (hormone like substance) when activated.
  • Cytokines stimulate right B cells to divide into plasma cells which make antibodies.
  • Cytokines stimulate macrophages to carry out phagocytosis more vigorously.

Killer T cells:

  • Search for cells invaded by pathogen and displaying antigens.
  • Attach to infected cells and secrete toxins e.g. hydrogen peroxide - kills body cell and pathogen.

Memory T cells:

  • These cause the response to be faster the second time round.
Immunity

Allergies

Allergies

Immunity

Antibodies

Antibodies

Immunity

Antibody classes

Antibody classes

Immunity

B lymphocytes

B lymphocytes

Immunity

Immune system

Immune system

Immunity

Phagocytosis

Phagocytosis