Lymphocytes

Innate Immune Cells

• Include macrophages, granulocytes, neutrophils, eosinophils, basophils, mast cells, dendritic cells, and natural killer (NK) cells.
• Main features: fast, non-specific, and generic immune response.
• Innate immune cells involved in phagocytosis: macrophages, neutrophils, and eosinophils.

Adaptive Immune Cells

• Composed of highly specialized cells like B lymphocytes and T lymphocytes.
• B lymphocytes are responsible for humoral immunity through antibody production.
• T lymphocytes carry out cell-mediated immunity, targeting infected cells.

Phagocytosis and Immunological Defense

• Process by which macrophages, neutrophils, and eosinophils engulf and digest pathogens.
• Natural killer cells perform immunological surveillance, detecting virus-infected cells.
• Physical barriers include skin, epithelial membranes, hair, and one-way urine flow.

Antimicrobial Substances

• Natural substances that provide defense include HCl, lysozyme, natural antibodies, saliva, interferons, and complement proteins.

Inflammation

• Characterized by rubor (redness), calor (heat), dolor (pain), and tumor (swelling).

Antigen-Specific Immunity

• Unique to specific antigens and involves a time lag to maximum response.
• Offers immunological memory for faster responses upon re-exposure.

Lymphocyte Characteristics

• Normal range: 1.5-3.5 x 10^9/L in blood; can persist for many years.
• Central role in protecting against infections; slightly smaller than neutrophils.
• Large and round nuclei characteristic of lymphocytes; heterogeneous based on lineage and CD molecules expression.

Major Histocompatibility Complex (MHC)

• Cell surface proteins that present intracellular material to differentiate self from non-self.
• Found in all vertebrates; in humans, encoded by Human Leukocyte Antigen (HLA) genes.
• MHC-I is present on all nucleated cells; MHC-II is on antigen-presenting cells (APCs).

T Lymphocytes Development

• Produced and mature in the thymus, where they undergo positive and negative selection.
• CD4+ T helper cells and CD8+ cytotoxic T cells recognize MHC-II and MHC-I, respectively.

Functions of T Helper and Cytotoxic Cells

• TH lymphocytes aid in activating other immune cells by recognizing MHC-II.
• TC lymphocytes eliminate infected cells by recognizing MHC-I and inducing apoptosis.

B Lymphocytes Development and Function

• Produced and mature in the bone marrow, circulating in blood, spleen, and lymph nodes.
• Recognize antigens via surface antibodies (B cell receptors) and secrete antigen-specific antibodies.

Plasma Cells and Antibody Production

• Plasma cells can secrete up to 2000 antibodies per cell per second for a limited time.
• Initial antibody production is IgM, followed by IgG after class switching.

Memory B Cells

• Confer immunological memory for rapid responses upon subsequent infections.
• Found in the spleen and lymph nodes, express high levels of IgA, IgG, and/or IgE after class switching.

Mechanisms of Antibody Action

• Opsonization enhances phagocytosis; antibodies coat antigens for better recognition.
• Complement activation leads to the lysis of pathogens, augmenting immune response.
• Neutralization prevents toxins and pathogens from exerting harmful effects.

Summary of True/False Statements

• B-cells express CD19 on their surface: true.
• Plasma cells secrete 200 antibodies per cell per second: false (2000).
• Antibodies defend through complement activation, opsonization, and neutralization: true.

Types of Immunity

• Cell-mediated immunity involves T-cells, targeting intracellular pathogens and tumors.
• Humoral immunity, primarily through plasma cells, protects against extracellular threats.

Innate Immune Cells

• Innate immune cells include macrophages, granulocytes, neutrophils, eosinophils, basophils, mast cells, dendritic cells, and natural killer (NK) cells.
• The innate immune response is characterized by being fast, non-specific, and generic.
• Phagocytosis is performed by macrophages, neutrophils (acting as antigen-presenting cells), and eosinophils.
• Immunological surveillance at body surfaces is primarily conducted by NK cells.

Physical Barriers and Natural Antimicrobials

• Physical barriers such as skin, epithelial membranes, hairs, and one-way urine flow play vital roles in defense.
• Natural antimicrobial substances include HCl, lysozyme, natural antibodies, saliva, interferons, and complement proteins.

Inflammation

• Four classical signs of inflammation are rubor (redness), calor (heat), dolor (pain), and tumor (swelling).

Adaptive Immune Cells

• Adaptive immunity involves specialized cells and is unique to specific antigens.
• B lymphocytes are responsible for humoral immunity, producing antigen-specific antibodies.
• T lymphocytes are involved in cell-mediated immunity, targeting infected cells.

Lymphocyte Characteristics

• Lymphocytes range from 1.5 to 3.5 x 10^9/L in blood and can persist for many years.
• They are classified into T cells and B cells, with T lymphocytes accounting for 75% of lymphocytes in the blood.
• Lymphocytes have a large, round nucleus and are slightly smaller than neutrophils.

Major Histocompatibility Complex (MHC)

• MHC molecules present intracellular material to facilitate identification of self vs. non-self.
• MHC-I is found on all nucleated cells, while MHC-II is found on antigen-presenting cells (APCs).
• The human equivalent of MHC is Human Leukocyte Antigen (HLA), which consists of HLA-A, HLA-B, and HLA-DR groups.
• HLA group alleles include 59 for HLA-A, 118 for HLA-B, and 124 for HLA-DR.

T Lymphocyte Activation and Function

• CD8+ T cells, or cytotoxic T lymphocytes, recognize MHC-I and eliminate infected cells via apoptosis.
• CD4+ T cells, or T helper lymphocytes, recognize MHC-II and assist other immune cells through cytokine release.
• Thymocytes undergo positive and negative selection during their maturation in the thymus; 95-98% die before reaching maturity.

B Lymphocyte Production and Function

• B lymphocytes are produced and mature in bone marrow and circulate in blood, spleen, and lymph nodes.
• They recognize antigens via surface antibodies (B cell receptors) and produce antigen-specific antibodies once activated.
• Plasma cells, derived from B cells, secrete up to 2000 antibodies per cell per second and have extensive rough endoplasmic reticulum for secretory function.

Antibody Functions

• Antibodies act through opsonization, complement activation, and neutralization of toxins.
• IgM is the initial antibody produced, followed by IgG after class switching; the presence of both indicates recent infection, while only IgG indicates a longer period since infection.

Memory B Cells

• Memory B cells confer immunological memory, ensuring rapid response during re-exposure to pathogens.
• They primarily reside in the spleen and can produce high levels of antibodies such as IgA, IgG, and IgE after class switch.

Summary of True/False Statements

• B-cells have CD19 on their surface - true.
• Plasma cells can secrete 200 antibodies per cell per second - false, it’s 2000.
• Antibodies defend through complement activation, opsonization, and neutralization - true.

Immune Responses Overview

• Cell-mediated response involves T-cells, targeting intracellular pathogens and cancers through specific MHC interactions.
• Humoral response involves plasma cells secreting antibodies to combat extracellular bacteria and foreign macromolecules.

Innate Immune Cells

• Primary innate immune cells include macrophages, granulocytes (neutrophils, eosinophils, basophils), mast cells, dendritic cells, and natural killer (NK) cells.
• Macrophages and neutrophils are involved in phagocytosis, a process where cells engulf and digest pathogens.
• Natural Killer cells conduct immunological surveillance, identifying and attacking infected or abnormal cells.
• Physical barriers to infection include skin, epithelial membranes, hairs, and mechanisms like one-way urine flow.
• Natural antimicrobial substances: HCl, lysozyme, natural antibodies, saliva, interferons, and complement proteins are critical defensive elements.

Adaptive Immune Cells

• Adaptive immunity relies on highly specialized immune cells, particularly B lymphocytes (produce antibodies) and T lymphocytes (cell-mediated responses).
• B lymphocytes are associated with humoral immunity while T lymphocytes focus on cell-mediated immunity.
• T-helper cells (CD4+) assist other immune cells, while cytotoxic T cells (CD8+) eliminate infected cells.

Characteristics of Innate Immune Response

• Features include being fast, non-specific, and generic in nature.
• Inflammation displays four classical signs: rubor (redness), calor (heat), dolor (pain), and tumor (swelling).

Lymphocyte Features

• Lymphocytes, slightly smaller than neutrophils, have a large, round nucleus occupying most of the cytoplasm.
• Normal range of lymphocytes in blood: 1.5-3.5 x 10^9/L, with a lifespan that can extend for many years.
• Lymphocytes are classified into two main types: T cells and B cells, crucial for immune response.

Role of Major Histocompatibility Complex (MHC)

• MHC molecules enable the immune system to distinguish self from non-self by presenting intracellular material at the cell surface.
• Found in all vertebrates, MHC genes in humans are referred to as Human Leukocyte Antigen (HLA), including HLA-A, HLA-B, and HLA-DR groups.
• MHC-I is present on all nucleated cells, while MHC-II is found on antigen-presenting cells.

T Cell Maturation and Function

• T cells mature in the thymus through a process of positive and negative selection, ensuring functional and self-tolerant T cell populations.
• CD8+ T cytotoxic cells target MHC-I complexes, while CD4+ T helper cells recognize MHC-II complexes.
• Cytotoxic T cells induce apoptosis in infected cells using perforin to create pores.

B Lymphocyte Overview

• B lymphocytes produce and mature in the bone marrow, circulating through blood, spleen, and lymph nodes.
• Their primary role is production of antigen-specific antibodies, which neutralize toxins and pathogens.
• Memory B cells, formed post-activation, ensure rapid responses upon re-exposure to pathogens.

Antibody Functions

• Antibodies perform key actions: opsonization enhances phagocytosis, complement activation leads to lysis of pathogens, and neutralization prevents pathogen action.
• Plasma cells secrete high volumes of antibodies (up to 2000 per second), primarily IgM initially, followed by IgG after class switching.

Summary of Immune Responses

• Cell-mediated responses protect against intracellular pathogens; humoral responses target extracellular bacteria and foreign particles.
• Both types of responses involve complex interactions between various immune cells, receptors, and signaling molecules, ensuring effective immune defense.

Explore the fascinating world of innate and adaptive immune cells in this quiz. Test your knowledge on various immune cell types, their functions in phagocytosis, and the body's defense mechanisms. Dive into the specifics of B and T lymphocytes and discover how they contribute to immunity.