Defensive Strategies - Adaptive Immune Response

Defensive Strategies -2: The Adaptive Immune Response

• The adaptive immune response is highly specific and has memory, distinct from the innate response.
• It is triggered by antigen presentation.
• Antigen-presenting cells (APCs) play a crucial role in initiating the adaptive response.
• Antigens, along with epitopes (the active part of the antigen), are involved.
• Antibodies are produced as part of the response.
• Major Histocompatibility Complex (MHC) class 1 and 2 molecules are essential components.
• Vaccines stimulate immunity.
• Herd immunity is a concept related to the collective protection of a population.
• Novel pathogens and zoonotic diseases are important considerations.

Adaptive Immune Response -Cells

• Lymphocytes (T and B cells) are derived from the lymphoid line (differentiated from myeloid line).
• T cells mature in the thymus.
• B cells mature in the bone marrow.
• Helper T cells play a key role in organizing both cellular (cytotoxic T lymphocytes) and humoral responses (through B cells).

T Cells

• T cells are derived from the thymus.
• Two basic types are helper T cells (Th cells) and cytotoxic T cells (Tc cells).
• Th cells are marked by CD4+.
• Tc cells are marked by CD8+.
• Helper T cells are critical coordinators of the adaptive immune response, though vulnerable to attack by HIV, the Human Immunodeficiency Virus.

B Cells

• B cells originate in bone marrow and mature there.
• They produce humoral responses, including plasma cells and memory cells.
• Plasma cells, the effector cells, produce antibodies.
• Memory cells provide a long-lasting response to repeated encounters with the same antigen.
• Plasma cells have a short lifespan, undergoing apoptosis (programmed cell death).

Antigens and Epitopes

• Antigens are molecules that react with preformed antibodies.
• Most antigens are proteins, both intrinsic and extrinsic.
• Epitopes are the portions of antigens that antibodies bind to.

Antibodies

• Antibodies are soluble molecules produced in response to antigens.
• Their key property is the ability to bind specifically to the antigen that prompted their production.
• Antibody-antigen complexes are formed.
• Antibodies are also known as immunoglobulins (Ig).
• There are five antibody classes: IgG, IgM, IgA, IgD, and IgE. Each has a distinct role in immune responses.

MHC Molecules

• MHC (Major Histocompatibility Complex) molecules are crucial for presenting antigens to T cells.
• MHC class 1 molecules present intrinsic (internal) antigens.
• MHC class 2 molecules present extrinsic (external) antigens.
• MHC molecules are involved in tissue typing and graft acceptance.

Response to Pathogens

• The body has responses (cellular and humoral) to intrinsic (intracellular) and extrinsic (extracellular) pathogens, activating different cell types.

Definitions

• R₀ (pronounced R-naught) is the basic reproduction number.
• It represents the average number of secondary infections caused by one infected individual in a wholly susceptible population. This number is indicative of a pathogen's transmissibility.
• Vaccination efforts aim to reduce R₀ below 1.

Vaccine

• Vaccine is a microbial antigen preparation (inactivated or weakened) to stimulate immunity.
• Edward Jenner developed the first vaccine to protect against smallpox.
• Several diseases have been significantly reduced due to vaccines (notably smallpox).

Herd Immunity

• Herd immunity occurs when a substantial portion of the population is immune to a pathogen, protecting those individuals who cannot be vaccinated.
• A high herd immunity level controls the spread of infectious disease.

Epidemics

• Epidemics involve a sudden increase in the prevalence (incidence) of a disease.
• Prevalence is the proportion of infected individuals in a group.
• Severity can be measured by factors including mortality rates, R₀, and herd immunity levels.

Zoonoses

• Zoonoses are diseases transferable from animals to humans.
• Many emerging infectious diseases are zoonotic in origin.
• Zoonotic transmission occurs through various methods.

Other Aspects of Immunity

• Factors relating to vaccine technology, epidemiology, and transmission patterns are part of studying immunity.