Immunology and blood plasma

What is an antigen and how does it activate T and B cells?

An antigen is a substance that activates T and B cells by binding to specific cellular receptors on the lymphocyte surface at the epitope.

Epitope

The specific part of an antigen that binds to receptors on T and B lymphocytes to trigger an immune response.

Innate (Non-specific) Immunity

General defense mechanisms like mechanical barriers (skin), chemical barriers (stomach acid), inflammation, phagocytosis, fever, and natural killer (NK) cells.

Antigen Presenting Cells (APCs)

Cells like macrophages that detect, engulf, digest pathogens, and present their antigens on the surface using MHC molecules.

Major Histocompatibility Complex (MHC)

Molecules on cell surfaces that display antigen fragments for recognition by T cells; essential for immune response.

• There are two classes:

  1. MHC I

  2. MHC II

Class I MHC

Found on all nucleated cells; present endogenous (intracellular) antigens to cytotoxic T cells.

Class II MHC

Found only on APCs; present exogenous (extracellular) antigens to helper T cells.

Cell-Mediated Immunity

Immune response involving direct cell-to-cell contact where T cells become activated upon binding to antigen:MHC complexes on APCs.

How many antigens can one T cell recognize?

One T cell recognizes a specific, single antigen.

Cytotoxic (Killer) T Cells (CD8 T cells)

T cells that proliferate upon activation, bind to cells showing non-self antigens, and secrete perforin to create holes in infected or damaged cells, causing apoptosis.

Helper T Cells (CD4 T cells)

T cells that secrete cytokines to activate other lymphocytes, including cytotoxic T cells and B cells, coordinating the immune response.

Why is HIV infection dangerous in terms of T cells?

HIV targets CD4 helper T cells, preventing activation of cytotoxic T cells and B cells, weakening the immune system.

B lymphocytes (B cells)

White blood cells responsible for producing antibodies (immunoglobulins) in response to specific antigens, with help from helper T cells.

What happens to B cells once activated?

They rapidly proliferate and differentiate into plasma cells that secrete up to 2000 antibodies per second.

• These antibodies bind to their specific antigens on pathogens and help eliminate them through hagglutination, precipitation, or neutralization.

Plasma cells

Differentiated B cells that produce and secrete large quantities of antibodies targeting specific antigens.

Humoral Immunity

Immunity mediated by antibodies circulating in bodily fluids that bind to pathogens to neutralize, precipitate, or agglutinate them.

Is humoral immunity the same as cell-mediated immunity?

No. Humoral immunity involves antibodies produced by B cells to target pathogens in body fluids, while cell-mediated immunity involves T cells that directly attack infected or abnormal cells.

What are memory lymphocytes?

Long-lived B and T cells that remain active after initial antigen exposure and enable a faster, stronger immune response upon re-exposure.

Blood plasma

The liquid portion of blood, about 92% water, containing dissolved proteins, gases, nutrients, electrolytes, and waste, which suspends formed blood elements.

What are the three major types of plasma proteins produced by the liver?

Albumins, globulins, and fibrinogen.

Albumins and globulins

Plasma proteins important for transporting free fatty acids, hormones, drugs, fat-soluble vitamins, and antibodies in the blood.

Fibrinogen

A plasma protein essential for blood clotting.

Why must plasma electrolytes be tightly regulated?

They are charged particles in blood and must be kept regulated because imbalances can alter resting membrane potentials and blood pH, disrupting normal cell function.

• includes calcium, phosphate, bicarbonate, chloride, sulfate, hydorgen