Avian immune system / Immunity

  Avian immune system

System of biological structure and cellular process in birds as defense system. It resembles to the mammals due to the common reptilian ancestor. Generally it is divided into two types

•   Innate immunity : immunity that is gained by birth
•      Acquired immunity: immunity that is drained during the adaption in the environment 
  
  
  

Structure of avian immune system: It is composed by immune organs, immune cells and immune mediators

Immune organs : It has 3 types

•      Primitive germinative organs
•     Primary organs
•     Secondary organs

Primary organs: It involves yolk sac , fetal liver , bone marrow .  The main function is to produce undifferentiated and unprogrammed cells .

Primary central maturation lymphoid organs: It involves thymus and bursa of fabricius

Thymus : it act as endocrine gland which secrete thymosin or thymopoietin autocoids . under the influence of this hormone thymus maturate and differentiated the T- lymphocytes .It has antibody mediated immunity.

Bursa of fabricius  : it also act as a endocrine gland which secrete urospectrin hormone under the influence of these hormone  B lymphocyte is maturated and differentiated.

Secondary lymphoid organs

1.     GALT:  it includes gastric tubular glands, esophageal tonsils, ileocecal tonsils, payers of patches , Meckel's diverticulum.  These are responsible for digestive local immunity

2.      HALT: Harderian gland and CALT

Harderian gland is present on the ventral of eyeball within the eye orbit. It open in the nictitating membrane. Its secretion lubricates the third eyelid. It also produce IgA and other immunoglobulins .

CALT is predominant in turkey

3.     BALT : it is responsible for the respiratory tract immunity

4.     SALT : it is responsible for skin immunity

5.     Spleen: it has white and red pulp. White pulp produce T lymphocytes and red pulp produce B lymphocytes. It is also responsible for Hemopoietic activity,  Ag processing and Ab production

6.     Mural lymphoid nodules  : mural lymphoid gland is associated with lymph vessels which is predominant in the pelvic cavity region.

7.     Pineal gland is present in cerebral hemisphere and cerebellum.it act as alight sensor.

Immune cells

It has 3 types

1.     RBC

2.     Thrombocytes

3.     Leucocytes

1.     Avian RBC: nucleated , MHC class I, may have immune function

2.     Avian thrombocyte: phagocytic action, Hemostasis

3.      Avian leucocytes

        i.            Heterophils :phagocytic

      ii.            Eosinophils : increase in parasitic manifestation

    iii.            Basophils : phagocytic action

    iv.            Monocyte and macrophages

      v.            Lymphocyte

Lymphocyte

1.     T lymphocytes: maturation in thymus

     5  types   : T helper cells 

                    : T cyto-toxic cells

                    : T suppressor cells

                    : T delayed cells

                    : Memory T cells

2.     B lymphocytes: Bursa of fabricius

a. Plasma cells

b. Memory B cells

3. Non B non T lymphocytes

a. Killer cell

b.  Natural killer cells

T lymphocyte

Origin :Bone marrow, maturation thymus

1.     T helper cell: secrete lymphokines

a. Type 1 :responsible for macrophage activation , B cell proliferation

b. Type 2 : regulation of antibody formation

2.     T-cyto-toxic cells:  recognize antigen ,lyses

 infected cells

3.     T suppressor cells :suppresses B and T cells

4.      T delayed cells :  predominant during chronic inflammation and delayed hypersensitivity

5.     Memory T cells : rapid potent reaction in succeeded infection by same pathogen

B lymphocytes

1.     B lymphocyte :  origin bone marrow maturation in Bursa of fabricius

:Antibody mediated response

:contain Ig D so that it can directly bind to virus or virions .

2. Plasma cells : originate from activated B cells in presence of IL2

                            : it helps in formation of different antibody

3. Memory B cells:  it is transformed by the B lymphocytes in presence of IL 1 and IL 5 . It has higher affinity to previously invading antigen

Non B non T lymphocytes

1. Killer cells : responsible for antibody dependent cell mediated cytotoxicity

    a     :Kill target cells without participation of complement

         b  : active in competing against viral infection

2. Natural killer cells : Destroy permanent virus infected and cancerous cells

§   virus induced activity is mediated by interferon

Avian immune mediators

Ø   cytokines: activated protein secreted by  T and B lymphocytes , macrophages , NK cells etc. it act as a chemical messenger : lymphokines secreted by lymphocytes and monokines is secreted by the macrophages . 

Ø Interferons : Non antigen glycoprotein, act on cell not  on virus  so it is species specific not virus specific.

   It gives  Response to viral or certain non viral inducer

3 types

1.     Alpha interferons :  produce by B lymphocytes and macrophages

2.     Beta interferons    : produce by  fibroblast and epithelial cells

3.     Gamma interferons:  produce by T lymphocytes