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02. SPECIFIC IMMUNITY

 

1) SPECIFIC IMMUNE RESPONSE is a physiological response to foreign material and acts to eliminate the nonself.

 

2) The main cell involved is the SMALL LYMPHOCYTE

 

Beneficial & harmful effect of specific immune response

 

Beneficial effects

Harmful effects

1. protects from infection

2. removes altered & old red cells, necrotic tissue

3. protects against tumors

1. destruction of tissues (hypersensitivity)

2. immune response to harmless antigens (allergy )

3. Immune response to self antigens (autoimmunity).

 

CARDINAL FEATURE OF SPECIFIC IMMUNITY

 

1) SPECIFICITY-Specific for distinct antigens

 

2) DIVERSITY-capable of recognizing a variety of antigens. (Al least 109different antigens.)

 

3) MEMORY-has memory for a past contact antigen and responds by rapid and larger response.

 

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4) SELF TOLERANCE-recognizes and responds to antigens that am foreign or non-self

 

5) AMPLIFICATION-increase no. of lymphocytes specific for a antigen

 

6) REGULATION –well controlled ,does not destroy the normal tissues of the body

 

 

The specific immune response has two types

 

  • Humoral immunity   :   Mediated by B lymphocytes
  • Cell-mediated immunity   :   Mediated by T lymphocytes.

 

PHASES

Humoral immunity

Cell-mediated immunity

RECOGNITION PHASE

  • B lymphocytes recognize antigen by antibodies (B cell receptors) on their surface Membranes
  • Each B lymphocyte clone has surface antibodies specific to a single antigen (really a single epitope).
  • Different lymphocyte clones have surface antibodies specific to different antigens.
  • T lymphocytes recognize antigen by T cell receptors (TCR)
  • TCR recognize only linear peptides.(proteins from pathogens have to be processed and cut up into peptides)
  • TCR recognize antigen only its conjunction with Major Histocompatibility complex (MHC) on the cell surface
  • TCR play a role in defense against intracellular pathogens, where peptides from the pathogen are presented on the surface, of the host cell.

ACTIVATION PHASE

  • B cell activation needs help from T helper lymphocytes.
  • costimutatory surface molecule on both T helper & B cells interact each other
  •                      ↓
  • T helper cells secrete cytokines( interferon γ) and IL4
  •                      ↓
  • promote the proliferation of B cells, give hundreds of similar B lymphocytes

For activation of T cell need

  • TCR binding to antigen presented by MHC molecules
  • the CD4 or CD8 molecule binding to the MHC molecule
  • Also Co-stimulatory surface molecule on the T cell and the other cell must interact.

T cell activation also needs help from helper cells.

T helper cells →secrete IL-2 →other T helper cells and T cytotoxic cells become activated, proliferate and differentiate.

EFFECTOR PHASE

  • Some of the B lymphocytes differentiate into PLASMA CELLS→ Secret antibodies
  • others become long lived MEMORY CELLS
  • Plasma cells are the effectors cells of humeral immunity
  • Antibodies are ineffective in dealing with antigens inside cells(eliminating antigens when they are found outside cells)
  • T cells deal with pathogens that invade and live inside cells such as viruses,intracellular bacteria and intracellular parasites.
  • That is why T cells are programmed to recognize antigen only in conjunction with MHC molecules on the surface of cells
02. SPECIFIC IMMUNITY 02. SPECIFIC IMMUNITY Reviewed by Radiology Madeeasy on April 13, 2010 Rating: 5
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