Immune system

2 types of lymphocytes

B cells and T cells

lymphocytes

a type of leukocyte central to the adaptive immune response

all lymphocytes originate from ___ in the ___

hematopoietic cells, bone marrow

B cells mature in the ___

bone marrow

T cells migrate from bone marrow to the ___ to mature

thymus

main function of B cells

produce antibodies (immunoglobins) that bind to specific antigens on pathogens

humoral immunity (B-cell / antibody-medicated)

targets extracellular pathogens (bacteria, toxins, free viruses)

B cells being activated leads to -

plasma cells secrete antibodies, memory b cells form

antibodies neutralize, ___, ___, and ___.

opsonize, agglutinate, activate complement

opsonization

tags the pathogen so phagocytes can recognize and eat it more easily.

agglutinate

sticking or clumping together of particles

Plasma cells

Short-lived antibody factories

memory B cells

Long-lived cells that remember the antigen for faster future responses

Cell-mediated Immunity (T-cell)

Targets intracellular pathogens (viruses inside cells), infected cells, cancer cells

Cytotoxic T-cells (CD8+)

Directly kill infected cells using perforins and granzymes

Helper T cells (CD4+)

Release cytokines to coordinate immune response (activate B cells, macrophages, etc.)

Regulatory T cells

suppress over-reactions

MHC (Major Histocompatibility Complex)

protein “display platforms” found on the surface of cells, show pieces of antigens to T cells

MHC Class I

shows antigens inside the cell, cytotoxic T cells (CD8+) reads it

MHC Class II

shows pathogens from outside the cell, read by Helper T cells (CD4+)

Where are MHC Class II found?

found in APC’s/Antigen presenting cells (dendritic cells, macrophages, B cells)

Primary Response (First exposure)

slow, lower antibody peak, mostly IgM, produces memory cells

Secondary Response (re-exposure)

very fast, much higher and longer antibody peak, mostly IgG, driven by memory B and T cells

IgG vs IgM

both are antibody classes

IgM

first to be produced, great for starting the primary response and activating the complement system, large (pentamer - 5 units)

IgG

produced later - dominates secondary response, smaller (monomer), crosses placenta, long-term immunity

perforins

proteins released by cytotoxic T cells (CD8+) and natural killer cells that punch holes in the cell’s membrane for granzymes to enter the cell

granzymes

enzymes (proteases) released by cytotoxic T cells (CD8+) and natural killer cells that trigger apoptosis inside the target cell

protease

subgroup of enzymes that specifically break down proteins by cutting the peptide bonds between amino acids

Cytokines

Small signaling proteins (messenger molecules) released by many immune cells, especially helper T cells (CD4+)

Examples of cytokines

interleukins, interferons, tumor necrosis factor (TNF)

interleukins

Make T cells and B cells proliferate (multiply)

interferons

Activate macrophages and interfere with virus replication

Tumor Necrosis Factor (TNF)

Promotes inflammation and kills some tumor cells

Innate Immunity

Immediate defense to slow down or stop the infection, activates and guides the adaptive immune system

Physical & Chemical Barriers (First Barrier of Innate Immunity)

skin, Mucous membranes + mucus, cilia in respiratory tract (sweep out trapped particles), antimicrobial proteins (lysozyme in tears/saliva, defensins)

Cellular Components (Second Barrier)

macrophages, neutrophils, dendritic cells, natural killer cells, mast cells

macrophages

phagocytosis, antigen-presenting cells

neutrophils

phagocytosis, release nets to trap bacteria, most common WBC

dendritic cells

patrol and present antigens, bridge to adaptive immunity

natural killer cells

kill virus-infected and cancerous cells through perforins + granzymes (same as cytotoxic T cells)

mast cells

trigger inflammation by releasing histamine

Innate vs Adaptive

Innate = fast, non-specific, no memory

Adaptive = slow, specific, has memory