Cell Cooperation in Humoral Immunity

 Humoral Immunity or Antibody-mediated immunity (AMI) is the type of adaptive immunity that is mediated by soluble host proteins       

            called antibodies or immunoglobulins. produced by plasma cells (Type of B lymphocytes),In the peripheral immune organs (spleen, Lymph nodes and bone marrow)

  Because it is largely due to the presence of circulating antibody molecules in the serum, is also called circulating immunity or humoral immunity.

Cooperation between cells in humoral immunity include 3 groups of cells

         Group-1 APC (Macrophages -Dendritic cells - B lymphocytes)

Group-2 T helper cells (Th2)

Group-3 B-Lymphocytes

Steps of Cell Cooperation in Humoral Immunity

1-Primary immune response

2-Secondary immune response

1-    Primary immune response

A-Fragmentation, processing and displaying of antigen by APC 

              Professional APCs are very efficient at internalizing antigen; by phagocytosis forming phagosome then lysosome unit with phagosome containing antigen,

             Forming phagolysosome where proteolytic enzymes secreted to fragment antigen into small epitopes (each epitope of 6-8 A.A) at the same time MHC II with its invariant chain move from

             endoplasmic reticulum to golgi apparatus where it mature and loses its invariant chain, And liberated into cytoplasm within its membrane then MHC II unit with phagolysosome each  

             epitope enter on its specific groove of MHC II

            Finally MHC II with its specific epitope move to be presented on the surface of APC

            B-Migration of APC to drainage lymph node where T cells present

            The T helper cell bearing CD4 always recognizes and interacts with the antigen-class II MHC molecule complex on the membrane of the antigen-presenting cell by both receptors

            ( 2signals)T cell receptor (TCR) and CD4 , an additional co-stimulatory chemical signal  interleukin-1(3^rd signals)  is then produced by the antigen-presenting cell together with at least other   

            two adhesion  molecules (4^th&5^th signals)  between T h2 and APC , the sum of 5 signals

           C-Th2 Proliferation & Differentiation:

           Presence of 5 signals leading to activation and stimulation of the T h2  cells that undergo proliferation and differentiation into other 2 types of cells:

          i-Effector Th cell: secrete IL4,IL5,IL6,IL13

          ii- Memory Th cell

          D-Stimulation of B lymphocytes(colon) to produce monocolonal or polycolonal Antibodies:

          Each colon of B cell specific for one epitope

         B cell contacted the processed antigen on MHC-II displayed on APC (1^st signal)

         B cell stimulated from Il-1 secreted by APC (2^nd signal)

         B cell stimulated by IL4,IL5,IL6,IL13(3^rd,4^th,5^th signals) secreted by effector Th cell 

         Presence of 5 signals leading to activation and stimulation of the B cells that undergo proliferation and differentiation into other 2 types of cells

          Plasma cell: antibody producing cell specific to the processed antigen.

          Memory cell: play an important role in secondary immune response, has long life may reach 60 years or more

2-   Secondary immune response

2^nd exposure of the immune system to the same antigen

B cell act by one of other two way whether to be

APC

Antibody producing cell more rapidly than 1^st time

Characteristics of the primary response:  

·         Slow response

·         Low  titres and short lasting

  

Characteristics of the secondary response: 

·         Faster and more effective than primary response  

·         Larger titres are produced, and these last longer