The human immune system is a highly coordinated defense network that protects the body against infections, toxins, and abnormal cells. Advances in immunology have not only deepened our understanding of disease resistance but have also led to the development of vaccines, blood products, monoclonal antibodies, and life-saving plasma substitutes. Unit 3 explores the types of immunity, molecular structure of immune components, immunological reactions, and modern biotechnological tools such as hybridoma technology that have transformed healthcare.
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Types of Immunity: Humoral and Cellular Defense Mechanisms
Humoral Immunity
Humoral immunity is mediated by antibodies produced by B-lymphocytes. These antibodies circulate in blood and body fluids, recognizing specific antigens such as bacteria, toxins, and viruses. Once bound, antibodies neutralize pathogens, promote phagocytosis, or activate the complement system. This form of immunity is particularly effective against extracellular pathogens and is the basis for most vaccine-induced protection.
Cellular (Cell-Mediated) Immunity
Cellular immunity is governed by T-lymphocytes, especially cytotoxic T cells and helper T cells. This system plays a crucial role in eliminating intracellular pathogens such as viruses, cancer cells, and transplanted tissues. Unlike humoral immunity, cellular immunity does not rely on antibodies but instead uses direct cell-to-cell interactions and cytokine signaling.
Structure of Immunoglobulins: Antibody Architecture and Function
Immunoglobulins, commonly known as antibodies, are Y-shaped glycoproteins composed of two heavy chains and two light chains connected by disulfide bonds. Each antibody has:
Variable regions, responsible for antigen binding
Constant regions, which determine biological activity
Different classes of immunoglobulins—IgG, IgA, IgM, IgE, and IgD—serve distinct physiological roles. For example, IgG provides long-term immunity, IgA protects mucosal surfaces, and IgE is involved in allergic reactions. Structural integrity of immunoglobulins is essential for their therapeutic and diagnostic applications.
Major Histocompatibility Complex (MHC): Immune Recognition and Self-Identity
Structure and Function of MHC
The Major Histocompatibility Complex (MHC) consists of cell surface glycoproteins that present antigenic peptides to T cells. There are two main classes:
MHC Class I, present on all nucleated cells, present endogenous antigens
MHC Class II, present on antigen-presenting cells, present exogenous antigens
MHC molecules are central to immune recognition, transplant compatibility, and autoimmune disease development. Their polymorphic nature ensures diversity in immune responses among individuals.
Hypersensitivity, Immune Stimulation, and Immune Suppression
Hypersensitivity Reactions
Hypersensitivity reactions are exaggerated immune responses causing tissue damage. They are classified into four types (Type I–IV), ranging from immediate allergic reactions to delayed cell-mediated responses. Understanding these reactions is essential for managing allergies, autoimmune diseases, and transplant rejection.
Immune Stimulation and Suppression
Immune stimulation enhances immune responses using vaccines, adjuvants, or cytokines, while immune suppression involves drugs like corticosteroids and immunosuppressants to control autoimmune diseases or prevent organ rejection. Both strategies are critical in clinical therapeutics.
Preparation of Immunological Products
Vaccines and Toxoids
Vaccines are biological preparations containing attenuated, inactivated, or subunit antigens that stimulate protective immunity. Toxoids are inactivated bacterial toxins used to induce immunity against toxin-mediated diseases such as tetanus and diphtheria.
Antitoxins and Serum Products
Antitoxins are antibody preparations used for passive immunity in emergency situations. Serum-derived immune products are obtained from immunized humans or animals and require careful purification to ensure safety.
Storage Conditions and Stability of Vaccines
Vaccines are highly sensitive to temperature, light, and contamination. Most vaccines require storage at 2–8°C to maintain potency. Cold chain maintenance is critical, as improper storage can lead to loss of immunogenicity and vaccine failure. Stability testing ensures safety and effectiveness throughout shelf life.
Hybridoma Technology: Monoclonal Antibody Production
Production and Purification
Hybridoma technology involves fusing antibody-producing B cells with immortal myeloma cells to form hybrid cells capable of continuous monoclonal antibody production. These antibodies are purified using chromatographic techniques to achieve high specificity and purity.
Applications
Monoclonal antibodies are widely used in:
Cancer therapy
Autoimmune disease management
Diagnostic assays
Targeted drug delivery
They represent one of the most significant breakthroughs in biotechnology and personalized medicine.
Blood Products and Plasma Substitutes
Blood Products
Blood products include plasma, albumin, clotting factors, and immunoglobulins used in trauma care, hemophilia, and immune deficiencies. These products undergo strict screening and purification to prevent disease transmission.
Plasma Substitutes
Plasma substitutes such as dextrans and gelatin solutions are used to restore blood volume during shock or surgery when blood transfusion is not immediately available. They provide temporary circulatory support without immunological compatibility issues.