Immunology- Pt 1A

Infectious Disease: General Info

• Infectious disease requires a susceptible host and pathogen to be in the same environment at the same time.
• The immune system prevents infection and consists of cells, tissues, and molecules that mediate resistance to foreign elements.
• The immune response is a coordinated reaction of immune cells and molecules to antigens.
• Immunology is the study of the immune system, including its responses to microbial pathogens and damaged tissues and its role in disease.
• An antigen is a molecule that induces an immune response when introduced into the body, generating antibodies.
• Epitopes (or antigenic determinants) are parts of an antigen responsible for inducing the immune response and binding to lymphocyte receptors and antibodies.

Immune System: General Info

• The immune system must discriminate foreign elements from its own components to prevent autoimmunity.
• Autoimmunity occurs when the immune system attacks its own cells, leading to autoimmune disorders/diseases.
• Immune responses should only be generated when components of the immune system come into contact with non-self-elements, such as antigens or microbes.
• Inflammation causes pain, swelling, and redness.

Cellular Origins

• All cells of the immune system originate from hematopoietic cells, which come from bone marrow.
• Hematopoietic cells differentiate into either common lymphoid progenitor or common myeloid progenitor.
• Common lymphoid progenitor is the source of B-cells and T-cells, which are part of adaptive immunity, as well as NK cells and ICL.
• Common myeloid progenitor is the source of mast cells, basophils, dendritic cells, monocytes (macrophages), eosinophils, and neutrophils.

Cells of the Immune System

• Granulocytes: neutrophils, basophils, and eosinophils
• Lymphocytes: NK cells (part of innate immunity), T-cells and B-cells (part of adaptive immunity)
• Others: mast cells, monocytes/macrophages, and dendritic cells

Innate vs. Adaptive Immunity

• Innate immunity involves a non-specific immune response, always active, with a fast response time and lacks memory.
• Examples of innate immunity include inflammation, complement, and physical barriers (such as skin or stomach pH).
• Adaptive immunity involves a specific immune response, only active when in contact with antigens, with a slow response time and has memory.
• Examples of adaptive immunity include humoral immunity and cellular immunity.

Neutrophils

• Neutrophils have a segmented nucleus and granules in their cytoplasm.
• Roles: antimicrobial effectors, particularly in acute bacterial infections and inflammation.
• Mechanisms: phagocytosis, degranulation, and neutrophil extracellular trap formation.

Eosinophils

• Eosinophils have a segmented nucleus and granules in their cytoplasm, which are visibly pink/orange.
• Roles: antiparasitic effector, some antiviral action, and an allergy role.
• Mechanisms: degranulation and very limited phagocytosis.

Basophils

• Basophils have a segmented nucleus and granules in their cytoplasm, which are visibly purple.
• Roles: mediator of inflammation.
• Mechanisms: degranulation.
• Found in tissue, not typically in blood.

Mast Cells

• Mast cells have a segmented nucleus and granules in their cytoplasm, which are visibly purple.
• Roles: immune surveillance, mediator and amplifier of inflammation and allergy.
• Mechanisms: detection of threats and release of inflammatory mediators via degranulation (vasoactive amines) or synthesis of lipid mediators and cytokines.
• Found in tissue and connective tissue.

Macrophages

• Macrophages are monocytes that have left the blood and gone to the tissue, primarily part of the innate immune response.
• Roles: immune surveillance, moderate antimicrobial capacity, and limited antigen presentation.
• Mechanisms: detection of threats and release of inflammatory mediators, and phagocytosis.
• Can differentiate into dendritic cells.

Dendritic Cells

• Roles: immune surveillance and antigen processing and presentation.
• Mechanisms: endocytosis, phagocytosis, and detection of threats and release of inflammatory mediators.
• Can sometimes be phagocytic, but primary role is antigen presenting.
• Capture microbes, break them down, and present their antigens to T-cells, initiating the adaptive immune response.

NK (Natural Killer) Cells

• NK cells are lymphocytes that lack antigen receptors.
• Roles: destruction of virally infected or abnormal host cells (including tumor cells).
• Mechanisms: recognition of virally infected or abnormal host cells and targeted release of cytotoxic granules.
• Induce apoptosis.

Lymphocytes (T-cells and B-cells)

• Roles: recognition of specific antigens/epitopes via TCR (T cell receptors) and BCR (B cell receptors) within adaptive immunity.
• T cells produce cytokines.
• B cells produce antibodies.
• Mechanisms: activation and regulation of cell-mediated and antibody responses; memory cells.
• Each T cell and B cell have multiple receptors on their surface, but each cell will only have specificity to 1 thing.

Immune System: Cell to Cell Communication

• Receptors are expressed on the surface of a cell or in intracellular compartments.
• Ligands are molecules that activate receptors, can be soluble or membrane-bound.
• Ligands can be time-consuming to travel to receptors, so cytokines can be used instead for a faster response time.
• Cytokines are proteins with functions of cell growth and activation.
• Cytokines can differentiate into T-cells.
• There are 2 types of cytokines: Interleukins (used for communication between cells) and Chemokines (used for chemotaxis).