Overview Of Immune System

Functions of the Immune System

• Recognizing microbes or tumors.

• Preventing and eliminating infections.

• Providing future protection (e.g., vaccination)

Importance of the Immune System

• Specificity and memory in adaptive immunity.

• Responses like inflammation and immunopathology (e.g., hypersensitivity, immunodeficiency, autoimmunity).

• Issues in modern medicine: graft rejection, transfusion reactions

Innate Immunity:

Immediate, lacks memory, uses pattern recognition receptors.

Adaptive Immunity

Delayed response, builds memory, uses antigen-specific receptors.

Lymphocyte Lineage

B,T, NK cells

B cells

Humoral immunity, antibody production

T cells

Cell-mediated immunity

CD4+ T cells (helper)

Aid B cells and phagocytes

CD8+ T cells (cytotoxic)

Kill infected cells

NK cells

Part of innate immunity, kill infected host cells

Types of Adaptive Immunity

Humoral Immunity and Cell-Mediated Immunity

Humoral Immunity

Antibodies neutralize extracellular microbes

Cell-Mediated Immunity

T cells target intracellular microbes

Why Innate Immunity Is the Early Line of Defense

Innate immunity provides immediate protection against a broad range of pathogens using barriers, phagocytic cells, and soluble mediators.

Role of Antibodies in Eradicating Extracellular Microbes?

Neutralization, Opsonization, Complement Activation

Neutralization:

Antibodies block microbes from infecting cells.

Opsonization

Enhance phagocytosis of microbes.

Complement Activation

Trigger pathways that lyse pathogen

Distinctions Between Humoral and Cell-Mediated Immunity

• Humoral Immunity: Mediated by B cells and antibodies; targets extracellular pathogens.

• Cell-Mediated Immunity: Mediated by T cells; targets intracellular pathogens like viruses.

NK Cells:

Part of innate immunity, lack antigen-specific receptors, and kill infected or stressed cells

T/B Lymphocytes

Part of adaptive immunity, possess antigen-specific receptors, and mediate long-term immune responses

CD4+ T Cells (Helper T Cells):

Assist B cells in producing antibodies and help phagocytes destroy ingested microbes.

CD8+ T Cells (Cytotoxic T Cells)

Kill cells harboring intracellular pathogens, such as viruses.

Adaptive Immune Response Timeline

Activation and differentiation of lymphocytes typically take 72–96 hours after initial exposure to the antigen.

PRRs

Recognize general microbial patterns

BCRs and TCRs

Recognize specific antigens with high precision, enabling targeted immune responses

Memory Cells

After an infection, the adaptive immune system retains memory B and T cells, enabling faster and stronger responses upon re-exposure to the same pathogen.

Innate Immunity:

Uses pattern recognition receptors (PRRs) to identify general patterns found in pathogens (pathogen-associated molecular patterns, PAMPs).

Adaptive Immunity:

Involves B-cell receptors (BCRs) and T-cell receptors (TCRs), which recognize specific antigens and epitopes.