Question

Non-specific immunity: 1st & 2nd line of defense. Specific immunity: 3rd line of defense.

While chopping an onion, you inadvertently cut your finger and a pathogen enters the cut. Recalling what you learned about non-specific and specific immunity, explain the non-specific and specific immune responses that occur at the site of this trauma.

Answer 1

• Immune response is initiated when; the body encounters any foreign molecules acting as exogenous or endogenous antigens).
• Immune system is the ability of the body to protect itself from invasion of foreign molecules such as pathogens. Immunity is the protective state of the body against infection.
• The two major components of immunity or immune response are, innate immunity and acquired immunity.
• The innate immunity or non-specific immunity acts as the first and second line of defenses, provides barrier against the foreign substances.

• Innate immunity is in born immunity and act as first line of defense. Innate immunity is non-specific, and include:

  1) Anatomical barriers or physical barrier include a) .skin- epidermis layer of skin has protective waterproofing keratin protein and dermis layer bear sebaceous glands which produce sebum, that inhibit growth of many microorganisms. B) mucous membrane- are washed and protected by mucous, tears or saliva. Also has ciliated epithelial cells that entraps microbes.

  2) Physiological barriers include body temperature, pH (potential of hydrogen), soluble molecules like lysozymes, interferons.

  3) Inflammatory response- complex sequence of events, resulting after pathogen invasion through a wound or damage. Results in four typical cardinal signs, rubor (redness), tumor (swelling), calor (heat) and dolor (pain).

  4) Phagocytic response- phagocytosis is mediated by endocytosis process of phagocytic cells like macrophages and neutrophils.

• Various cytokines released from specific cells, like interleukins (IL), tumor necrosis factor alpha (TNFα), activates the production of mature phagocytic cells, like neutrophils, macrophages and dendritic cells and induce their migration to the site of infection or invasion.
• Phagocytic cells, engulf the foreign substances by phagocytosis or endocytosis.
• The phagocytosed molecules processed and, then the peptide fragments of antigens are expressed through membrane bound glycoproteins called major histocompatibility complex (MHC).

• The third line of defense or acquired immunity is then initiated:
• Acquired immunity is also called adaptive immunity.
• Acquired immunity is not present from birth and is initiated on exposure to a foreign molecule or non-self-substance, or antigen of microorganisms, pathogens, or any foreign molecules. Hence it is also sometimes designated as “specific immunity”.

• The antigenic polypeptide bound to MHC molecules further induces B-lymphocytes (designated from Bursa of Fabricus in birds, in humans generated in bone marrow) and T-lymphocytes (lymphocytes maturing in thymus), generating humoral or cell mediated immune responses, as well as immunogenic memory. Such specific activations lead to clonal selection, clonal expansion and clonal deletion.
• T cytotoxic cells recognizes type I MHC molecules bound antigenic peptides, and co-stimulatory responses. They contribute to the cell mediate immunity. Tc , then differentiates into memory cells and effector cells called cytotoxic T-lymphocytes (CTLs). CTLs then further recognizes MHC-I complexes bound to the target cell, and thus destroy the target cell.
• B-cells differentiates into memory B-cells and effector B cells (or plasma cells). Plasma cells release antibodies. Antibodies, released to the plasma, tissue fluid and lymph, contribute to humoral immunity.