Adaptive Immunity Quiz

Adaptive Immunity - Specific Body Defense System

• Adaptive immunity is a specific body defense system.
• Adaptive immunity relies on a functional thymus and the conversion of stem cells to B cells and T cells.
• These cells contribute to antibody production, cellular immunity, and immunological memory.
• Adaptive immunity involves a reaction and interaction with substances the body identifies as non-self.

Components of Adaptive Immunity

• Components of adaptive immunity include the development of lymphocyte populations, the course of the adaptive immune response, immunological memory, and the overall innate and adaptive immune response.

Innate vs. Acquired (Specific) Immunity

• Innate immunity consists of the first and second lines of defense—skin, mucous membranes, secretions, reflexes, and normal microbiota.
• Acquired (Specific) immunity consists of the third line of defense—T cells, B cells, and antibodies.
• The second line of defense includes inflammation, phagocytes, fever, complement system, interferons, and NK cells.

Lymphocytes

• Lymphocytes are the smallest leukocytes.
• They circulate in the blood and lymph and can migrate into tissues and lymphoid organs.
• Lymphocytes provide immune defense against specific targets they are programmed for. 
• Types of lymphocytes include B cells, T cells, and natural killer (NK) cells.
  • B cells mature in bone marrow, produce antibodies, circulate in the blood, and are responsible for antibody-mediated (humoral) immunity.
  • T cells mature in the thymus, directly destroy their target cells by releasing chemicals that punch holes, and are responsible for cell-mediated immunity.
  • NK cells are involved in innate immune responses, using perforin and granzymes.

B cells and T cells

• B cells are first discovered in the bursa of Fabricius (in birds) and mature in bone marrow.
• T cells mature in the thymus. T cells have two subpopulations: Helper T cells (TH cells) and Cytotoxic/Killer T cells (Tc cells).
• Some lymphocytes mature in the bone marrow and become B cells, while others are processed in the thymus and become T cells.

B Cells and T Cells Maturation

• Mature lymphocytes that haven't encountered their antigen are known as naïve lymphocytes.
• Activated lymphocytes that have differentiated into effector lymphocytes. 
• Some activated B cells and T cells develop into memory cells.
• Some activated B cells differentiate into plasma cells that secrete antibodies and present antigens to T cells.

Activated T Cells

• Activated T cells have three main classes: Cytotoxic T cells, Helper T cells, and Regulatory T cells.

B Cell and T Cell Receptors

• Each B and T cell has receptors to bind to specific types of antigens on their surface.
  • B cell receptors are complex transmembrane proteins made of membrane immunoglobins (usually IgM and IgD) and disulfide-linked heterodimers (Iga/Igβ). These Ig molecules have short cytoplasmic tails that need Iga/Igβ to transduce signals. 
  • T cell receptors (TCR) recognize peptide-MHC complexes on antigen-presenting cells (APCs). TCR complex contains the recognition domain (TCR) and accessory molecules (CD3 and zeta chain) to convey signals. TCR only has one antigen binding site.

CD4 and CD8

• CD4 is found on helper T cells and regulatory T cells.  
• CD8 is found on cytotoxic T cells.
• CD4 and CD8 proteins play roles in signal transduction and promote adhesion of T cells and antigen-presenting cells (APCs).

Two Arms of Adaptive Immunity

• Adaptive immunity has two arms: antibody-mediated (humoral) immunity and cell-mediated immunity.
  • Antibody-mediated immunity involves the production of antibodies in response to antigens. These antibodies circulate in blood and body fluids and enter tissues. Naïve B cells bind to the antigen, proliferating into lymphoblasts and differentiating into plasma cells secreting specific antibodies, and memory cells.
  • Cell-mediated immunity involves the production of activated T cells. Activated T cells detect and eliminate cells harboring intracellular microbes or tumor cells. It plays a major role in transplant rejection.

Antibody Structure

• Antibodies are proteins found in blood serum and other body fluids, secreted by plasma cells in response to antigens.
• Antibodies bind specifically to antigens.
• Structure includes a variable region to determine specificity (paratope) and a tail portion influencing functionality (based on its tail regions).
• Antibodies have four polypeptide chains: two identical light(L) chains and two identical heavy(H) chains.
• Disulfide bonds join the polypeptide chains within the antibody molecule as well as non-covalent interactions.

Antibody Classes and Subclasses

• Antibody classes (IgG, IgM, IgA, IgD, IgE) are based on differences in amino acid sequences in the constant region of the heavy chain. Subclasses show minor variations in the amino acid sequences of the heavy chains' constant regions.
  • IgG, the most common antibody, is effective against various antigens, has monomers, fixes complement, and is a good opsonin.
  • IgA is the next most common antibody and frequently found in secretions (body fluids) as a dimer.
  • IgM is the primary antibody formed by a naïve B cell when exposed to an antigen for the first time, is mostly a pentamer (five domains), and is a good agglutinating antibody.
  • IgD is found on B cell surfaces as a monomer and helps with antigen receptor function.
  • IgE is found in low serum levels; it binds to basophils and mast cells before interacting with an antigen;involved in allergic reactions and parasitic infections.

Antigen-Presenting Cells (APCs)

• Antigen-presenting cells (APCs) display antigens complexed with MHC on their surface.
• APCs process and present antigens to T cells.

Antigen Processing and Presentation – exogenous and endogenous

• Exogenous: Foreign antigens are taken up by APCs via endocytosis, processed, and combined with class II MHC molecules, displayed on the APC surface triggering TH cell activation.
• Endogenous: Intracellular antigens are processed in the cytoplasm, combined with class I MHC molecules, and then transported to the cell surface for Tc cell activation.

Other Important Terms:

• Clonal selection is a process in which lymphocytes are created to recognize a specific antigen. Lymphocytes are either destroyed via clonal deletion of those that recognize self or those that proliferate and differentiate into a clone of effector and memory cells.
• T cell receptor (TCR) is a receptor for antigen presentation on MHC molecules.
• Major Histocompatibility Complex (MHC) plays a key role in antigen presentation—a complex of proteins crucial to adaptive immune cells recognizing self versus foreign cells and helping immune cells discriminate.

Test your knowledge on adaptive immunity with this quiz that covers plasma cells, T cells, and their roles in the immune system. Questions explore key concepts such as antigen presentation and lymphocyte maturation. Ideal for students of immunology or related fields.