Adaptive Immunity

• Immunology is the study of the immune system, focusing on the body's defense against pathogens and harmful substances.

Adaptive Immunity

• Adaptive immunity, or acquired immunity, is a specific defense system that develops over time with exposure to antigens.
• Lymphocytes (B cells and T cells) are involved, recognizing and remembering specific pathogens.
• This immunity provides long-lasting protection.
• Humoral and cell-mediated immunity are its two main types.
• B cells produce antibodies in humoral immunity to neutralize pathogens in bodily fluids.
• T cells directly kill infected cells or activate other immune cells in cell-mediated immunity.
• Specificity, diversity, memory, and self-tolerance are key characteristics.
• Specificity ensures tailored immune responses to particular antigens.
• Diversity allows response to a wide range of antigens.
• Memory enables a faster, stronger response upon re-exposure.
• Self-tolerance prevents the immune system from attacking the body's own cells.

Innate Immunity

• Innate immunity is the first line of defense, providing immediate protection against pathogens.
• It is a non-specific defense mechanism, responding to a broad range of pathogens without prior exposure.
• Physical barriers (skin, mucous membranes), chemical barriers (enzymes, acidic pH), and cellular defenses (phagocytes, natural killer cells) are components of this immunity.
• Macrophages and neutrophils are phagocytes that engulf and destroy pathogens.
• Natural killer (NK) cells kill infected or cancerous cells by releasing cytotoxic granules.
• Inflammatory responses involve cytokine release and immune cell recruitment.
• Pattern recognition receptors (PRRs) recognize pathogen-associated molecular patterns (PAMPs) on pathogens, triggering immune responses.
• Cytokines like interferons and interleukins mediate communication and regulate immune responses.

Autoimmunity

• Autoimmunity occurs when the immune system attacks the body's own cells and tissues.
• This results in autoimmune diseases like rheumatoid arthritis, systemic lupus erythematosus (SLE), and type 1 diabetes.
• Various organs and systems are affected, leading to chronic inflammation and tissue damage.
• The exact causes are not fully understood, but genetic and environmental factors contribute.
• Molecular mimicry, where immune responses cross-react with self-antigens, is a mechanism of autoimmunity.
• Failure of T cell tolerance, where autoreactive T cells are not eliminated or suppressed, is another mechanism.
• B cells can produce autoantibodies that target self-antigens, causing tissue damage.
• Treatment involves immunosuppressive drugs to reduce immune system activity and inflammation.

Vaccination Principles

• Vaccination induces adaptive immunity against a pathogen by administering a weakened or inactive form, or a part of it (antigen).
• The goal is to stimulate antibody and memory cell production, providing long-lasting protection.
• Live attenuated, inactivated, subunit, and mRNA vaccines are types of vaccines.
• Live attenuated vaccines contain weakened pathogens that can still replicate but are less likely to cause disease.
• Inactivated vaccines contain killed pathogens that cannot replicate but still elicit an immune response.
• Subunit vaccines contain only specific antigens from the pathogen, such as proteins or polysaccharides.
• mRNA vaccines contain messenger RNA that instructs cells to produce a specific antigen, triggering an immune response.
• Herd immunity occurs when a large proportion of the population is vaccinated, reducing the spread of the pathogen and protecting unvaccinated individuals.
• Vaccines have been highly effective in preventing and eradicating many infectious diseases, such as polio, measles, and smallpox.

Immune Response Mechanisms

• The immune response involves complex interactions of cells, molecules, and processes to eliminate pathogens and maintain homeostasis.
• Antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells capture, process, and present antigens to T cells.
• T cells recognize antigens presented on MHC molecules on APCs.
• Helper T cells (CD4+ T cells) and cytotoxic T cells (CD8+ T cells) are the main types of T cells.
• Helper T cells secrete cytokines that activate other immune cells.
• Cytotoxic T cells directly kill infected or cancer cells by releasing cytotoxic granules.
• B cells differentiate into plasma cells that produce antibodies, which bind to antigens and neutralize pathogens.
• Antibodies can activate complement, enhancing phagocytosis and promoting inflammation.
• The complement system can directly kill pathogens by forming membrane attack complexes (MACs).
• Regulatory T cells (Tregs) suppress immune responses and maintain self-tolerance, preventing autoimmune reactions.
• Memory cells (both T cells and B cells) provide long-lasting immunity for a faster, stronger response upon re-exposure.

B Cells

• B cells are lymphocytes playing a crucial role in humoral immunity.
• They develop in the bone marrow, maturing into immunocompetent cells that recognize specific antigens.
• B cells express B cell receptors (BCRs) on their surface, which are antibodies binding to specific antigens.
• Upon encountering its cognate antigen, a B cell internalizes, processes, and presents it to helper T cells.
• Helper T cells provide signals (cytokines) that activate B cells, leading to proliferation and differentiation into plasma cells and memory B cells.
• Plasma cells are short-lived, secreting large amounts of antibodies that circulate in bodily fluids.
• Antibodies neutralize pathogens, activate complement, and enhance phagocytosis.
• Memory B cells are long-lived, providing immunological memory for a faster, stronger antibody response upon re-exposure.
• B cells undergo affinity maturation, increasing antibody affinity over time due to somatic hypermutation and clonal selection.
• B cells can act as antigen-presenting cells (APCs), initiating T cell-mediated immune responses.

T Cells

• T cells are lymphocytes central to cell-mediated immunity and regulation of other immune responses.
• They develop in the thymus and mature into immunocompetent cells that recognize specific antigens presented on MHC molecules.
• Helper T cells (CD4+ T cells) and cytotoxic T cells (CD8+ T cells) are the main types of T cells.
• Helper T cells recognize antigens presented on MHC class II molecules on antigen-presenting cells (APCs).
• They secrete cytokines that activate other immune cells such as B cells, macrophages, and cytotoxic T cells.
• Th1, Th2, Th17, and T regulatory cells (Tregs) are subsets of helper T cells, each with distinct cytokine profiles and functions.
• Cytotoxic T cells recognize antigens presented on MHC class I molecules on infected or cancerous cells.
• They kill target cells by releasing cytotoxic granules containing perforin and granzymes, which induce apoptosis.
• T cell activation requires interaction of the T cell receptor (TCR) with the MHC-peptide complex and costimulatory signals from APCs.
• T cells undergo positive and negative selection in the thymus to ensure self-tolerance and the ability to recognize foreign antigens presented on MHC molecules.
• T regulatory cells (Tregs) suppress immune responses and maintain self-tolerance, preventing autoimmune reactions.
• Memory T cells (both helper and cytotoxic T cells) provide long-lasting immunity for a faster and stronger response upon re-exposure.