Cellular Pathogens and the Immune System

Vocabulary-style flashcards covering types of pathogens, the innate and adaptive immune responses, the lymphatic system, types of acquired immunity, and disease control strategies based on the lecture notes.

Pathogen

The whole disease-causing organism or infectious agent.

Antigen

A molecule found on the surface of a pathogen that stimulates an immune response.

Self-antigens ($MHC$ molecules)

Proteins on the membrane of body cells that immune cells check to distinguish self from non-self.

Cellular pathogens

Living organisms made of cells, such as bacteria, fungi, protozoa, and worms, that can often reproduce independently.

Non-cellular pathogens

Infectious agents not made of cells, such as viruses and prions, that are not considered living and need a host to reproduce.

Binary fission

The process by which one bacterial cell divides into two identical cells.

Prions

Infectious proteins that do not reproduce like living organisms but convert normal proteins into abnormal ones via a chain reaction.

Innate immunity

The body's first and second lines of defence; it is present from birth, immediate, non-specific, and non-adaptive.

Lyzozomes

Enzymes in tears and saliva that are capable of destroying bacterial cell walls.

Natural Flora

Non-pathogenic bacteria on the skin, gut, and vagina that inhibit the growth of pathogens by competing for space and nutrients.

Macrophages

Leucocytes that perform phagocytosis, digest pathogens, and present antigens to Helper T cells.

Neutrophils

The most abundant white blood cells and the first to arrive at an infection to rapidly engulf bacteria; they have a short lifespan.

Mast cells

Cells that release histamine to cause inflammation and are important in allergic reactions.

Natural Killer ($NK$) cells

Cells that destroy virus-infected and cancer cells by releasing proteins that trigger apoptosis.

Apoptosis

Programmed cell death.

Complement proteins

Proteins in blood plasma that punch holes in bacteria, attract immune cells, and increase phagocytosis.

Interferons

Proteins released by virus-infected cells that warn neighbouring cells and slow viral replication.

Phagocytosis

The process by which certain white blood cells, such as macrophages and neutrophils, engulf and destroy pathogens.

Lymphatic system

A network of vessels, nodes, and organs that returns tissue fluid to the blood, filters pathogens, and provides sites for immune cell activation.

Primary Lymphoid Tissue

Tissues where lymphocytes develop and mature, specifically the bone marrow and thymus.

Antigen-Presenting Cells ($APCs$)

Cells like macrophages, dendritic cells, and B cells that display pathogen fragments on their surface using $MHC II$ proteins to activate the adaptive response.

Adaptive immunity

The third line of defence; it is highly specific, develops after exposure, and forms immunological memory.

Helper T Cells ($CD4$)

Immune system 'managers' that release cytokines to activate B cells and Cytotoxic T cells.

Cytotoxic T Cells ($CD8$)

Cells that detect infected body cells and destroy them by releasing perforin and cytotoxins to trigger apoptosis.

Humoral Response

The adaptive immune response that targets pathogens outside body cells using B lymphocytes and the production of antibodies.

Plasma Cells

Daughter cells of B cells that produce thousands of antibodies every second.

Antibody

A Y-shaped protein with variable regions at the tips that bind to specific antigens to neutralise, agglutinate, or opsonise pathogens.

Agglutination

A process where one antibody binds multiple pathogens, causing them to clump together so they are easier for macrophages to engulf.

Natural Active Immunity

Long-term immunity gained after the body naturally encounters a pathogen and produces its own antibodies and memory cells.

Artificial Passive Immunity

Immediate but temporary protection gained by receiving pre-made antibodies from another source, such as snake antivenom.

Herd Immunity

Occurs when enough people in a population are immune, interrupting disease transmission and protecting vulnerable individuals.

Zoonosis

A disease that spreads from animals to humans, such as COVID-19 or Rabies.

ELISA ($Enzyme-Linked Immunosorbent Assay$)

A lab method that uses enzyme-linked antibodies to produce a colour change when specific antigens or antibodies are detected.