IMMUNITY: 

 • The ability of the host to fight the disease-causing organisms, 

 • conferred by the immune system. 

 .Immunity is of two types: 

 • Innate immunity 

 • Acquired immunity. 

Innate immunity 

• Non-specific type of defence, 

 • Present at the time of birth. 

 .Innate immunity is accomplished by providing different types of barriers to the entry of the foreign agents into our body. 

 • Innate immunity consists of four types of barriers.

 These are —

        • Physical barriers: 

                Ø Skin 

                 Ø Mucus coating of the epithelium lining 

        • Physiological barriers: 

                Ø Acid in the stomach, 

                Ø saliva in the mouth, 

                Ø tears from eye

•    cellular barriers: 

                   Ø Leukocytes (WBC) à polymorpho-nuclear leukocytes (PMNLneutrophils) 

                   Ø monocytes and 

                  Ø natural killer (type of lymphocytes) 

                 Ø macrophages in tissues 

        • Cytokine barriers: 

                

                 Ø INTERFERON à

                        • Virus-infected cells secrete low molecular weight proteins 

                       • protect non-infected cells from further viral infection.

ACQUIRED IMMUNITY: 

      • Pathogen specific. 

      • Characterised by memory.

     • PRIMARY RESPONSE: 

           Ø when a pathogen attacks the host body for the first time 

          Ø the response of immune system is of LOW INTENSITY.

      • SECONDARY RESPONSE 

          Ø When the same pathogen attack, response of immune system is highly intensified (our body has memory of first attack of pathogen) 

         Ø This response is also called the ANAMNESTIC RESPONSE. 

Antibody mediated immune response/humoral immune response (AMIS) 

        • The primary and secondary immune responses are carried out with the help of two special types of lymphocytes present in our blood, i.e., Blymphocytes and T -lymphocytes. 

              • The B-lymphocytes produce proteins in response to pathogens into our blood to fight with them. à ANTIBODIES. 

              • The T-cells do not secrete antibodies but help B cells produce them. 

              • Each antibody molecule has four peptide chains, 

                        o two small called light chains 

                        o two longer called heavy chains.

                        o an antibody is represented as H2L2.

CMI: CELL MEDIATED IMMUNE RESPONSE

            • CMI response is given by T-lymphocytes. 

            • CMI is responsible for organ transplant rejection and graft rejection. 

            • Ability of T-cells to recognise self-cell/nonself cell is the basis of attacking invaders/pathogen but this characteristics creates problem during organ transplant therefore T-cells attack on transplanted organ/grafts and rejected the process. 

            • That’s why tissue matching, blood group matching are essential before undertaking any graft/transplant and even after this the patient has to take immunosuppressants all his/her life. 

THERE ARE TWO TYPES OF ACQUIRED IMMUNITY.

     • Active immunity: 

          Ø Antibodies are produced in the host body. 

          Ø Active immunity is slow 

         Ø takes time to give its full effective response. 

         Ø Vaccination or entry of pathogen into body during natural infection induce active immunity.

   • Passive immunity: 

         Ø When ready-made antibodies are directly given to protect the body against foreign agent is called PASSIVE IMMUNITY. 

The yellowish fluid colostrum secreted by mother during the initial days of lactation has abundant antibodies (IgA) to protect the infant therefore breast feeding is must for new born.
.

Colostrum and antibodies from placenta give passive immunity to new born and foetus respectively. 

.Rabies vaccine, tetanus vaccine and antivenom injection (in case of snake bite) give passive immunity as in passive immunity the antibodies are preformed so body’s immune response is quick.