12th Zoology

Secondary Lymphoid Organs

Secondary Lymphoid Organs

Mucosa associated lymphoid tissues (MALT) :

The mucosa lining the alimentary, respiratory, genitourinary and other
lumina and surfaces are constantly exposed to numerous antigens. These
areas are endowed with a rich collection of lymphoid cells, either specialized
aggregates as the Peyer’s patches or Scattered isolated lymphoid follicles
– collectively called the Mucosa associated lymphoid tissues (MALT).

Such lymphoid tissues in the gut are called Gut associated lymphoid tissue
(GALT) and those in the respiratory tract are called Bronchus associated
lymphoid tissue (BALT). MALT contains lymphoid cells as well as
phagocytic cells. Both B and T cells are present. The mucosa is endowed
with secretory IgA. The mucosal regions afford/confer protection from many
enteric and respiratory infections. (Secondary Lymphoid Organs)


The terms immunogen and antigen are often used synonymously.
However, these terms imply two closely related entities. The first describes a
molecule that provokes an immune response(immunogenicity) and hence is
called an immunogen. The other describes a molecule which reacts with the
antibody produced, or with the activated cellular constituents of cell
mediated immunity(antigenicity), and is referred to as an antigen. (Secondary Lymphoid Organs)

In contrast to this is the hapten. Haptens are small well defined
chemical groups such as dinitrophenol (DNP) which are not immunogenic on
their own but will react with preformed antibodies. To make a hapten immunogenic, it must be linked to a carrier molecule which is itself immunogenic.
Antigens are recognized not only by antibodies, but also by antigen
specific T cell receptors. In contrast to immunoglobulins, which usually
recognize intact antigens, T cell surface receptors recognize processed
antigens on the surface of antigen presenting cells. (Secondary Lymphoid Organs)

Related Topics in Zoology:

Bio Zoology All Important Topics

  1. Microbiology Introduction and History of Medical Microbiology

  2. Pasteur, Koch, Lister

  3. Structure of Viruses

  4. Viral genetics

  5. Virus Culture

  6. Viral Diseases

  7. Bacteria Structure Culture

  8. Bacterial Genetics

  9. Bacterial Diseases

  10. Protozoan microbiology

  11. Pathogenecity of Microorganisms

  12. Antimicrobial Resistance

  13. Antibiotics and Chemotherapy

  14. AIDS – HIV

Unit 3 – Immunology Topic List Zoology


  2. Acquired Immunity

  3. Structure and Functions of the Immune System

  4. Peripheral Lymphoid Organs

  5. Secondary Lymphoid Organs

  6. Antigenic determinants and epitopes

  7. Antibodies – Immunoglobulins

  8. Transplantation immunology

  9. Genetic basis of organ transplants

  10. Immune system disorders

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