Introduction to the Immunological System

Introduction to the Immunological System

• The presentation is given by Dr. Saúl Gallardo Aguilar from the Department of Microbiology, San Salvador, in February 2025.
• The general objective is to identify the elements that participate in the body's defense against disease, using basic knowledge.
• Immunity represents the body's capacity to resist or remain unaffected by a disease or process.
• It allows the organism to resist and defend itself from the aggression of foreign agents that generally produce disease.
• The term immunity includes all the properties of the host that confer resistance to an infectious agent, up to complete non-susceptibility.
• Immunology studies the immune system in all organisms and is a broad branch of biology and biomedical sciences.
• The immune system is a set of organs, tissues, and cells in vertebrates that recognize foreign elements and give a response.

Types of Immunity

• There is a need to distinguish between nonspecific and specific mechanisms when considering defenses against transmissible diseases

Innate Immunity

• Innate immunity is rapid, stops infection and is without memory, but is nonspecific
• Adaptive immunity is slow, clears the infection, has memory

Mechanisms of Innate Immunity

• Mechanisms include physiologic barriers at the point of entry, like skin and mucus membranes, and innate immunity mechanisms
• Innate immunity include phagocytic cells, phagocytosis, activation of the alternate complement pathway, inflammatory response, fever, interferons, and natural killer (NK) cells.
• The system of innate immunity uses receptors to recognize patterns, both soluble and attached to the membrane, to perceive invasive microorganisms.

A. Phagocytic Cells

• Phagocytic mononuclear cells are in blood, lymphoid tissue, liver, spleen, lung, and other tissues
• They are efficient at capturing and eliminating particulate material from lymphatic vessels and the bloodstream.
• An important function of the spleen is to filter microorganisms from the bloodstream.

B. Phagocytosis

• Functions of phagocytic cells include migration and chemotaxis.
• During phagocytosis cells are attracted to pathogens, ingest then destroy microbes.
• Phagocytosis can be affected by opsonization, which is when an antigen or particle is covered, and/or substances like antibodies.

C. Activation of the Alternative Pathway of the Complement

• The complement system comprises a group of proteins that enhance adaptive and innate immune responses to infection.
• Complement proteins have antimicrobial properties e.g. opsonization, bacterial lysis, amplification of inflammatory responses

Cytokines

• Cytokines are substances secreted by immune system cells that participate in both specific and nonspecific defenses.
• They include secretions that act on cells where they are produced, nearby cells to regulate activity, and modify effects of cells at a distance.

Inflammation

• Damaged cells and basophils release histamine, which dilates blood vessels attracts phagocytic cells.
• The increased blood flow heats the skin and delivers fluids and antibodies to the tissues.
• Edema occurs upon an increase of fluids and induces pain.

Fever

• Fever is controlled by a response from the hypothalamus to modify body temperature.

Types of Acquired/Adaptive Immunity

• Includes active immunity that generates antibodies with memory function, and passive immunity, which is temporary
• The organism acquires specific antibodies after effect passes with time.
• Active immunity can be natural, after surviving an infection, or artificial, through vaccination.
• Passive immunity can also be natural, transfer through the placenta, or artificial, through serum therapy

Mechanism of Specific Defence

• Immunity can be natural or acquired; the latter can be passive or active.
• Natural immunity does not require previous contact with the agent.

Passive Immunity

• Offers rapid yet short protection acquired during pregnancy and is reinforced through breastfeeding.
• It can also acquired also through serums or gamma globulins
• Gamma globulins are substances that produce antibodies to combat diseases produced by bacteria, but they act for a short time.

Active Immunity

• Immunity acquired through vaccines can for years if not for a lifetime
• This is based on lymphocytes and phagocytes such as macrophages and neutrophils.

Cellular Basis of the Immune Response

• B cells are lymphocytes that develop in bone marrow.
• B cells rearrange immunoglobulin genes and express single receptors for antigens on their cell surface.
• B cells migrate to secondary lymphoid organs, such as the spleen, can activate upon encountering an antigen, and turn into antibody generating plasma cell.
• T cells require maturation in the thymus and form various classes with specific functions.

Molecules for Recognition of Antigens and Antibodies

• The immune system, to properly respond to foreign antigens, needs a system of recognition that distinguishes with precision.
• Antibodies, or immunoglobulins, are produced by B lymphocytes. Each individual has a large reserve of different B lymphocytes, with a lifespan of days or weeks.
• You can find them in the bone marrow, lymph nodes, lymphoid tissue, and are associated with the intestine, the tonsils and the cecal appendix.

Classes of Immunoglobulins (antibodies)

• IgG is abundant in secondary responses, defends against viruses and bacteria, It passes through the placenta from mother to offspring
• IgM is effective in agglutination and complement fixation
• IgA secretions protect mucous membranes
• IgE is involved with allergies
• IgD acts as an antigen receptor on certain lymphocytes.

Antibody-Mediated Immunity (Humoral)

• Primary response happens when an individual encounters an antigen for the first time
• Antibodies become detectable in the serum in a few days or weeks, the first antibodies formed are IgM
• Secondary response is quicker and more concentrated compared to primary, in the case you encounter the same disease again months or years later.

Protective Functions of Antibodies

• Antibodies produce resistance to infection through opsonization of microorganisms
• Enhances phagocytosis, reducing their capacity to bind with cell receptor molecules.
• Antibodies are able to neutralize toxins from micro organisms to deactivate their hazardous effects.

The Complement System

• Includes serum proteins that function for defense systems of both innate and adaptive system
• Complement refers to these protein's ability to complement & augment immune components such as antibodies,
• Functions include lysis of cells especially bacteria and tumor cells, producing mediators that participate in inflammation/ attracting phagocytes
• It supports microorganism consolidation and the complex immunities for elimination by phagocyosis.

Cellular Immunity

• The antibody-mediated immunity is more important but cellular immunity usually provides protection for the infection and its recovery.
• Cellular immunity is essential for defending host against intracellular pathogens like viruses, fungal infections, and tumors.
• Conditions which can cause suppression of immune system will trigger aggressive infections of tumours which highlights it's significance

T Lymphocytes

• Proliferation and differentiation occurs inside the thymus, the main function of T cells is to perform the cell reactions.
• The cell reactions and the late reactions of hypersensitivity is produced from the antigens of parasites including fungi, viruses, and particular bacteria.
• Due to cellular immunity a notable probability to infections, and tumours can manifest

Regulatory Function

• Lymphocytes are the main regulation of immunity humoral
• Production of antibodies for lymphocyte B normally requires the assistance of lymphocytes T but antibodies are produced because of the T-dependent lymphocyte response

Cytokines in Cellular Immunity

• Cytokines are mediators-soluble for the defence host
• The fundamentals within effective mechanisms are the mechanisms and elimination of particular antigens and foreign antigens.

Hypersensitivity

• Excessive immune system response and bad reactions are denoted as Hypersensitivity which means its hostile to the host.
• The standard reactions only develop after the second exposure of the antigen
• The primary contact is the event that triggers sensitivity.

Types of Hypersensitivity Reactions

• Type 1, 2, and 3 is caused by antibodies but type 4 is caused by the cells.

Immune Response

• There are many diseases that cause deficiency within immunity which deform the hosts reaction towards the infection
• Anomalies such as granulomatous disease reduces action within the activity of bacterial action.
• VIH infection

T Lymphatic

• Original origin location is bone marrow, as it ages in the thymus
• Cytotoxic cells recognize affected cells and eliminates them
• There are various receptors such a Supressors and CD4 on these T lympocytes

Lymphocytes B

• After it ages within the bone marrow, it has receptors that assist with a specific Antigen.

• When the lymphocyte and the antigen connect lots of indentical cells are made leading to the cells specialzing within antibodies

• Cytotoxic cells as its developed like WBC's matures and becomes blood in the bone marrow but ages outside/ past the Thymus.

• When cytokines are triggered and lots are NK raises immunity when NK rises to the body fights cancer as stress can effect performance and cause Tumors.

• Macrophages engulf the foreign cells acting as an antigen which activates lymphocyte T helper-cells

MHC Definition

• Located as protein membrane and various within people the type of MHC within our species are called HLA.

Presentation by Dr. Saúl Gallardo Aguilar, this lesson introduces the immunological system and its role in defending the body against diseases. It explores the concept of immunity and its importance in resisting foreign agents. Immunology, the study of the immune system, is highlighted as a broad field within biology and biomedical sciences.