IMMUNOLOGY-4 NOTES 2026, Lecture notes of Nursing

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IMMUNOLOGY

Definition of terms

Immunity- a state of resistance or usceptibility exhibited by an individual to toxic molecules Immunology- the study of immune system,cells, organs and tissues Autoimmunity literally means “protection against self”; however, in practice it leads to “injury to self.”

• Molecules that can be recognized by the immunoglobulin receptor of B cells or by the T-cell receptor antigens(toxin or foreign substance).
• Antigens are substances that react with antibodies, while immunogens are molecules that induce an immune response.
• antigens are immunogens, and the terms are used interchangeably.

History

• The concept of immunity has existed since the ancient times.
• Chinese custom- children made resistant to smallpox by making them inhale powders made from the skin lesions of patients recovering from the disease.
• Edward Jenner - experiment injected the material from a cowpox pustule into the arm of an 8-year-old boy and demonstrated the lack of development of disease after subsequent exposure to smallpox. This was based on his observations that milkmaids who had suffered from cowpox never contracted the more serious smallpox.
• However, lack of knowledge of obvious disease targets and their causes, it was after nearly hundred years that this technique was applied to prevent smallpox.

The Immune System

• Immune system consists of lymphoid and reticuloendothelial ( mononuclear phagocyte system ) components and is responsible for immune response of the host.
• The lymphoid cells, which include lymphocytes and plasma cells, are responsible for conferring specific immunity.
• the reticuloendothelial system consists of phagocytic cells and plasma cells, is responsible for nonspecific immunity.
• These cells kill microbial pathogens and other foreign agents, and remove them from blood and tissues.
• Lymphoid tissues and organs include;
• 1. Thymus
• first lymphoid organ to develop. It reaches its
• maximal size at puberty and then atrophies,
• The thymus is a flat, biIobed organ situated above the heart.

4. Spleen

• The spleen is the largest lymphoid organ. high in the left abdominal cavity. 5. Mucosa-associated lymphoid tissues
• consist of the lymphoid tissues of the intestinal tract, genitourinary tract, tracheobronchial tree, and mammary glands.
• All of the MALT contain both T and B lymphocytes, and
• the latter predominate. Structurally, these tissues include clusters
• of lymphoid cells in the intestinal villi, tonsils, appendix, and Peyer’s patches(in the intestines). 6. Tonsils: These are present in the oropharynx and are predominantly populated by B lymphocytes. 7. Peyer’s patches: These are lymphoid structures that are found within the submucosal layer of the intestinal lining.

1. Lymphocytes

• The lymphocytes occupy a very special place among the leukocytes.
• ■ They participate in immune reactions due to their ability to interact specifically with antigenic substances and to react to nonself antigenic determinants.
• ■ They also contribute to the memory of the immune system.
• They differentiate from stem cells in the fetal liver, bone marrow, and thymus
• into two main functional classes: B cells and T cells. They are found in the peripheral blood and in all lymphoid tissues.
• The lymphocytes are classified depending upon where they undergo their development and proliferation: ( a) T lymphocytes or T cells undergoing development in the thymus or
• ( b) B lymphocytes, or B cells undergoing development in the bone marrow

1. Antigen-presenting cells

• Include ( a) macrophages and ( b) dendritic cells.
• Macrophages
• consists of monocytes circulating in the blood and macrophages in the tissues.
• The monocyte is considered a leukocyte in transit through the blood,
• which becomes a macrophage when fixed in a tissue.
• Monocytes and macrophages as well as granulocytes are able to ingest particulate matter (microorganisms, cells, inert particles) and for this reason are said to have phagocytic functions.

• 4. Effector cells that function to eliminate antigens
• A. Plasma cells
• Plasma cells originate from terminally differentiated B cells.
• ■ The main function of the plasma cells is to produce and secrete all the classes of immunoglobulins into the fluids
• around the cells.
• ■ They, however, do not express membrane immunoglobulins.
• ■ They have a short lifespan of 30 days during which they produce large quantities of immunoglobulins.
• B. Natural killer cells
• Natural killer (NK) cells are morphologically described as large granular lymphocytes. These cells are called natural killer
• cells due to their ability to kill certain virally infected cells and tumor cells without prior sensitization.
• NK cells comprise approximately 5–10% of peripheral lymphocytes and are found in spleen and peripheral blood.

• Basophils, on the other hand, are non-phagocytic granulocytes that function by releasing pharmacologically active substances from their cytoplasmic granules. These substances play a major role in certain allergic responses.
• Mast cells are the other granulocytic cells that have a role in he immune system. These cells are found in a wide variety of tissues, including the skin, connective tissues of various organs, and mucosal epithelial tissue of the respiratory, genitourinary, and digestive tracts.
• Mast cells, together with blood basophils, play an important role in the development of allergies.

• The main function of the immune system is to prevent or limit infections by pathogenic microorganisms, such as bacteria, viruses, parasites, and fungi.
• The recognition of microorganisms and foreign substances is the first event in immune responses of a host.
• The body’s defense mechanisms can be divided into: ( a) innate
• (natural) immunity and ( b) acquired (adaptive) immunity.

• Innate immunity shows the following features:
• It is due to the genetic and constitutional makeup of an individual. Prior contact with microorganisms or their products is not essential.
• acts as the first line of defense of the host immune system.
• The mechanisms involved in innate immunity are present in place even before exposure to the foreign agent. They are not specific to any infectious agent and do not seem to improve response on repeated exposures.
• Phagocytic cells (e.g., macrophages and neutrophils), barriers (e.g., skin and mucous membrane), and a variety of antimicrobial compounds synthesized by the host, all play important roles in innate immunity

Factors influencing innate immunity

• Age: Extremes of age make an individual highly susceptible to various infections. immature immune system in very young children and waning immunity in older individuals. The fetus-in-utero is usually protected from maternal infections by the placental barrier. However, human immunodeficiency virus (HIV), rubella virus, cytomegalovirus, and Toxoplasma gondii cross the placental barrier and cause congenital infections.
• Nutritional status:. Both humoral and cell mediated immunities are lowered in malnutrition.
• Hormonal levels: Individuals with certain hormonal disorders become increasingly susceptible to infection. For example, individuals suffering from diabetes mellitus, hypothyroidism, and adrenal dysfunction are increasingly susceptible to staphylococcal infection, streptococcal infection, candidiasis, many other microbial infections.
• Similarly, pregnant women are more susceptible to many infections due to higher level of steroid during pregnancy.

• ■ In addition, nonpathogenic organisms tend to colonize the epithelial cells of mucosal surfaces. These normal flora generally compete with pathogens for attachment sites on the epithelial cell surface and for necessary nutrients.
• Physiologic barriers:
• ■ Gastric acidity very few ingested microorganisms can survive the low pH of stomach contents.
• Interferons are secreted by cells in response to products of viral infected cells. These substances have a general antiviral effect by preventing the synthesis of viral structural proteins.
• Complement is a group of serum-soluble substances that when activated damage the cell membrane.
• Phagocytosis: a process of ingestion of extracellular particulate material by certain specialized cells, such as blood monocytes, neutrophils, and tissue macrophages. It is a type of endocytosis in which Invading microorganisms present in the environment are ingested by the phagocytic cells. In this process, plasma membrane of the cell expands around the particulate material, which may include whole pathogenic microorganisms to form large vesicles called phagosomes.
• Inflammatory responses: Tissue damage caused by a wound or by an invading pathogenic microorganism induces a complex sequence of events, collectively known as the inflammatory responses. The end result of inflammation may be the activation of a specific immune response to the invasion or clearance of the invader by components of the innate immune system. The four cardinal features of inflammatory responses are rubor (redness), calor (rise in temperature), dolor (pain), and tumor (swelling).

Mediators of inflammatory reactions

• ■ Histamine: IIt binds to receptors on nearby capillaries and venules, causing vasodilatation and increased permeability.
• ■ Kinins; inflammatory response. They are normally present in blood plasma in an inactive form. Tissue injury activates these small peptides, which then cause vasodilatation and increased ermeability of capillaries. Bradykinin also stimulates pain receptors in the skin. This effect probably serves a protective role because pain normally causes an individual to protect the injured area.
• ■ Acute-phase proteins: These include C-reactive proteins and mannose-binding proteins that form part of the innate immunity. These proteins are produced at an increased concentration in plasma during acute-phase eaction, as a nonspecific response to microorganisms and other forms of tissue injury. They are synthesized in the liver in response to cytokines called proinflammatory
• Cytokines; interleukin-1 (IL-1), interleukin-6 (IL- 6), and tissue necrosis factor (TNF). They are called proinflammatory cytokines because they enhance the inflammatory responses.
• ■ Defensins: They are cationic peptides that produce pores in membrane of the bacteria and thereby kill them.
• These are present mainly in the lower respiratory tract and gastrointestinal tract.