Specific Immunity

• Specific immunity involves responses to specific antigens

Terminology

• Important terms to be familiar with include antigen, antibody, agglutination, opsonization, apoptosis, neutralization, cytokines, humoral vs cell-mediated immunity, primary vs secondary immune response, and active vs passive immunity

Innate vs Specific Immunity

• Innate immunity uses the same process for every invader and is not specific
• Innate immunity occurs immediately with invasion or tissue damage
• Innate immunity does not provide memory
• Inflammation, phagocytosis, and complement are part of innate immunity
• Neutrophils, macrophages, and natural killer cells are involved in innate immunity
• Specific immunity is a specific response to a recognized antigen
• Specific immunity is acquired over time
• Specific immunity provides memory, known as the amnestic response
• Specific immunity produces antibodies
• T cells and B cells are key players in specific immunity
• Specific and innate immunity rely on each other in the immune response
• Antigen presentation by dendritic cells is one instance of the two systems interacting
• Antibody-dependent complement cascade and natural killing are other instances of the two systems interacting

Humoral Immunity

• Extracellular antigens are presented to B cells and T cells
• Antigen-presenting cells (APCs) include macrophages and dendritic cells
• B cells can directly bind to an antigen and present it
• MHCII (major histocompatibility complexes) are found on the surface of B cells and APCs
• T helper cells (CD4) recognize MHCII on B cells and APCs
• Helper T cells (CD4) interact with B cells
• T-dependent antigens are proteins
• T cells release cytokines
• T cells activate B cells, resulting in clonal expansion and enhanced phagocytosis
• B cells can become plasma cells or memory B cells
• T-independent antigens are polysaccharides
• B cells can be activated independently of T cells, but the immune response is weaker and doesn't provide memory
• Polysaccharides like LPS (endotoxin) can trigger this response
• B cells turn into plasma cells and produce antibodies
• Types of antibodies include IgM, IgG, IgA, IgE, and IgD
• IgM is the first antibody present in early immune responses
• IgG is the most common antibody, appears later in infection or in secondary exposure responses, and can pass through the placental lining
• IgA is found in mucosal surfaces
• IgE mediates allergies and hypersensitivities
• IgD acts as a receptor on B cells
• Antibodies perform agglutination, opsonization, ADCMC, neutralization, and complement activation
• Agglutination clumps antigens to inactivate them
• Opsonization identifies antigens for phagocytosis/lysis
• ADCMC (antibody-dependent cell-mediated cytotoxicity) enhances NK cell activity against large pathogens
• Neutralization prevents microbe attachment, stopping toxin function
• Activation of complement leads to complement action through the classical pathway

Cell Mediated Immunity

• Infected cells (intracellular pathogens) and cancerous cells are attacked by this immunity
• Cytotoxic T cells (CD8) recognize MHCI receptors on infected cells
• This induces apoptosis and releases interferons
• Leads to memory T cells
• Other types of T cells include regulatory/suppressor cells
• Suppressor cells help prevent immunity to self-antigens

Primary and Secondary Immunity

• Primary immunity is the initial response, with no previous exposure
• It is slower and relies on IgM first, then IgG
• Specific to each antigen
• Secondary immunity (anamnestic response) happens with subsequent exposures
• Natural immunity or vaccination can induce it
• It is actively acquired through exposure
• Specific to each antigen

Passive Immunity

• Passive immunity provides a temporary supply of antibodies
• It is limited in time and amount, and uses the mother's memory
• It is transferred in domestic animals mostly in the colostrum, but also transplacentally (IgG)
• Can also directly provide antibodies in plasma or hyper-immune serum

Cytokines

• Cytokines are chemical messengers of communication, communicating by attaching to a receptor
• Cytokine storm is a severe immune reaction in which the body releases too many cytokines at one time
• Interferons are a cytokine specific to viruses and are short-lived