MCAT Immune Cells (+Inhibition)

Competitive inhibition

• No change in Vmax or kcat

• Km increases

• Lineweaver-Burk: same y-intercept, slope increases, x-intercept shifts toward zero. Key idea: inhibitor competes with substrate at active site; can be overcome with high [S].

Noncompetitive inhibition (pure)

• Vmax decreases

• kcat decreases

• Km unchanged.

• -Burk: y-intercept increases, x-intercept unchanged, slope increases. Key idea: inhibitor binds allosteric site equally well to E and ES.

Uncompetitive inhibition

• Vmax decreases

• kcat decreases

• Km decreases

• Lineweaver-Burk: parallel lines (slope unchanged), y-intercept increases, x-intercept shifts left. Key idea: inhibitor binds only ES complex, trapping substrate.

Mixed inhibition

• Vmax decreases

• kcat decreases

• Km changes (increases or decreases depending on binding preference)

• Lineweaver-Burk: lines intersect left of y-axis but not on axes. Key idea: inhibitor binds both E and ES with different affinities.

Neutrophils

• Innate immune system; first responders to bacterial infection

• Perform phagocytosis and destroy pathogens with granules/enzymes

• Most abundant white blood cell

• Key idea: acute bacterial infections → increased neutrophils.

Macrophages

• Innate immune system

• derived from monocytes

• Perform phagocytosis and antigen presentation (MHC II) to helper T cells

• Release cytokines to activate immune response

• Key idea: bridge innate and adaptive immunity.

Monocytes

• Innate immune system

• circulate in blood and differentiate into macrophages or dendritic cells in tissues

• Phagocytic

• Key idea: precursor immune cell.

Dendritic Cells

• Innate immune system (with adaptive-linking role)

• major antigen-presenting cells (APCs)

• Present antigens on MHC II to activate helper T cells

• Key idea: strongest activators of naïve T cells.

Natural Killer (NK) Cells

• Innate immune system

• destroy virus-infected and cancer cells without prior sensitization

• Detect low MHC I expression and induce apoptosis using perforin/granzymes

• Key idea: innate cytotoxic lymphocyte.

Mast Cells

• Innate immune system

• involved in allergic reactions and inflammation

• Release histamine and heparin upon activation

• Key idea: mediate immediate hypersensitivity reactions.

Basophils

• Innate immune system

• involved in allergic responses and parasite defense

• Release histamine

• Rare in blood

• Key idea: similar function to mast cells.

Eosinophils

• Innate immune system

• defend against parasites and contribute to allergic reactions/asthma

• Contain toxic granules

• Key idea: elevated in parasitic infections and allergies.

B Cells

• Adaptive immune system

• mature in bone marrow

• Differentiate into plasma cells that produce antibodies and memory B cells

• Recognize free antigens directly

• Key idea: humoral immunity.

Plasma Cells

• Adaptive immune system

• activated B cells specialized for antibody secretion

• Produce large amounts of antibodies

• Key idea: effector B cells.

Memory B Cells

• Adaptive immune system

• long-lived B cells formed after exposure to antigen

• Enable rapid secondary immune response

• Key idea: basis of vaccination memory.

Helper T Cells (CD4+)

• Adaptive immune system

• coordinate immune responses by releasing cytokines

• Activated by MHC II on APCs

• Key idea: activate B cells, macrophages, and cytotoxic T cells.

Cytotoxic T Cells (CD8+)

• Adaptive immune system

• kill infected or cancerous cells using perforin/granzymes

• Recognize antigen on MHC I

• Key idea: adaptive cell-mediated killing.

Regulatory T Cells (Tregs)

• Adaptive immune system

• suppress immune responses and maintain self-tolerance

• Prevent autoimmunity

• Key idea: immune “brakes.”

Memory T Cells

• Adaptive immune system

• long-lived T cells that respond rapidly upon re-exposure to antigen

• Key idea: faster secondary response.