Adaptive Immunity PDF

Immunity Adaptive Immunity Lec-3- Acquired Immunity (= Adaptive or Specific Immunity): Adaptive immunity is the specific immune response that is acquired over time after exposure to a pathogen or through vaccination. It is characterized by specificity, memory, and the ability to distinguish...

Immunity Adaptive Immunity Lec-3- Acquired Immunity (= Adaptive or Specific Immunity): Adaptive immunity is the specific immune response that is acquired over time after exposure to a pathogen or through vaccination. It is characterized by specificity, memory, and the ability to distinguish between self and non-self. There are two main types of adaptive immunity: Humoral Immunity: B cells and antibodies; targets extracellular pathogens. Cell-Mediated Immunity: T cells; targets intracellular pathogens and abnormal cells. Both types of adaptive immunity work together to protect the body from pathogens and provide long-term immunity after an initial infection or vaccination. Characteristics of Acquired Immunity: (i) Specificity: It is the ability to differentiate between various foreign molecules (foreign antigens). (ii) Diversity: It can recognise a vast variety of foreign molecules (foreign antigens). (iii) Discrimination between Self and Non-self: It can recognise and respond to foreign molecules (non-self) and can avoid response to those molecules that are present within the body (self) of the animal. iv) Memory: ( When the immune system encounters a specific foreign agent, (e.g., a microbe) for the first time, it generates immune response and eliminates the invader. This is called first encounter. The immune system retains the memory of the first encounter. As a result, a second encounter occurs more quickly and abundantly than the first encounter.  Certain cells of the bone marrow produce В lymphocytes and mature there. Since В lymphocytes produce antibodies, therefore, this immunity is called antibody mediated or humoral immunity. Humoral immunity or antibody-mediated immune system (AMIS) provides defence against most extracellular bacterial pathogens and viruses that infect through the respiratory and intestinal tract. There are two main types of adaptive immunity 1. Humoral Immunity (Antibody-Mediated Immunity) Primary Function: This form of immunity is mediated by B cells (B lymphocytes) and their production of antibodies. Mechanism: When B cells encounter a pathogen or foreign antigen, they become activated and differentiate into plasma cells that secrete antibodies. These antibodies bind to specific antigens, neutralizing the pathogen or marking it for destruction by other immune cells (such as macrophages or neutrophils). Target: Primarily effective against extracellular pathogens (e.g., bacteria, viruses outside of cells) and toxins. Memory: Memory B cells are generated, which allows for a faster and more robust response upon re-exposure to the same pathogen.  2. Cell-Mediated Immunity Primary Function: This immunity is mediated by T cells (T lymphocytes), which do not produce antibodies but instead directly attack infected or abnormal cells. Types of T-cells and their Functions: 1. Helper T cells (TH): TH cells are most numerous of the T cells. They help in the functions of immune system. They produce a growth factor that stimulates В-cell proliferation and differentiation and also stimulates antibody production by plasma cells; enhance activity of cytotoxic T cells. 2. Cytotoxic T cells (Tc) or Killer cells: These cells are capable of killing microorganisms and even some of the body’s own cells directly hence they are called killer cells. In addition, the cytotoxic T cell releases cytotoxic substances directly into the foreign cell. Almost immediately, the foreign cell becomes greatly swollen and it usually dissolves shortly thereafter. Thus they destroy body cells infected by viruses and attack and kill bacteria, fungi, parasites and cancer cells. 3-Memory T Cells (Primed Cells): These cells are also formed by T-lymphocytes as a result of exposure to antigen and remain in the lymphatic tissue (e.g., spleen, lymph nodes). They recognize original invading antigens even years after the first encounter. These cells keep ready to attack as soon as the same pathogens infect the body again. They proliferate and differentiate into cytotoxic T cells, helper T cells, suppressor T cells, and additional memory cells. 4. Suppressor Cells (Regulatory T cells (TR)): These cells are capable of suppressing the functions of cytotoxic and helper T cells. They also inhibit the immune system from attacking the body’s own cells. It is believed that suppressor cells regulate the activities of the other cells. For this reason, the suppressor cells are classified as regulatory T cells. Natural Killer (NK) Cells: NK cells attack and destroy target cells, participate in antibody dependent cell mediated cytotoxicity. They can also attack parasites which are much larger than bacteria.  Immunity can be classified into two broad categories: natural and artificial immunity, each with subtypes. Here's an overview: 1. Natural Immunity Natural immunity occurs without deliberate intervention. It is developed through exposure to pathogens during everyday life. Natural Active Immunity: o Definition: This type of immunity develops when an individual is exposed to a pathogen and the immune system responds by producing antibodies and memory cells. o Example: Recovering from a viral infection like chickenpox. After infection, the body builds immunity and remembers the virus, preventing future infections.  Natural Passive Immunity: o Definition: This type of immunity occurs when antibodies are passed from one individual to another naturally, without the recipient’s immune system having to respond actively. o Example: Maternal antibodies passed to a baby through placenta (during pregnancy) or through breast milk after birth. These antibodies provide the baby with temporary protection against certain infections. 2. Artificial Immunity Artificial immunity is acquired through deliberate exposure to a pathogen or its components, often through medical intervention.  Artificial Active Immunity: o Definition: This type of immunity develops when a person is exposed to a form of the antigen via vaccination, prompting the immune system to produce antibodies and memory cells. o Example: Vaccination with the measles, mumps, and rubella (MMR) vaccine. The vaccine contains weakened or killed pathogens or their components, stimulating an immune response without causing the disease itself.  Artificial Passive Immunity: o Definition: This type of immunity involves the direct transfer of antibodies to an individual, providing immediate but temporary protection. o Example: Receiving an antibody injection (e.g., antiserum for snake venom or rabies immunoglobulin after a potential rabies exposure). These pre- formed antibodies help neutralize the toxin or pathogen immediately, without the person’s immune system needing to produce them.