Immune System Practice Questions
20 free Immune System practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which type of white blood cell is the first to arrive at the site of an infection and is the primary component of pus?
- A Neutrophils
- B Monocytes
- C Basophils
- D Lymphocytes
Correct answer: Neutrophils
Neutrophils are the most abundant type of white blood cell and act as the first responders to bacterial infection. They eliminate pathogens through phagocytosis and the release of cytotoxic granules.
What is the primary function of B-lymphocytes in the adaptive immune response?
- A Producing antibodies
- B Killing virus-infected cells
- C Engulfing bacteria
- D Releasing histamine
Correct answer: Producing antibodies
B-lymphocytes, or B cells, are responsible for humoral immunity. When activated, they differentiate into plasma cells that secrete specific antibodies to neutralize pathogens.
Which of the following is considered a primary lymphoid organ where immune cells are produced or matured?
- A Spleen
- B Lymph nodes
- C Peyer's patches
- D Bone marrow
Correct answer: Bone marrow
Primary lymphoid organs include the bone marrow and the thymus. These are the sites where lymphocytes are generated (bone marrow) and mature (B cells in marrow, T cells in thymus).
Which class of antibodies is the most abundant in the blood and can cross the placenta to provide passive immunity to a fetus?
- A IgG
- B IgA
- C IgE
- D IgM
Correct answer: IgG
IgG is the most common antibody in circulatory system. Its unique ability to cross the placenta provides the newborn with maternal immune protection during the first few months of life.
The 'Innate Immune System' is characterized by which of the following?
- A Immediate, non-specific response
- B Memory of previous infections
- C Highly specific recognition of antigens
- D Production of long-lasting antibodies
Correct answer: Immediate, non-specific response
Innate immunity is the body's first line of defense, including physical barriers and general cellular responses. It does not provide long-lasting immunity or specific recognition like the adaptive system.
Which cell type is responsible for the rapid immune response upon re-exposure to a pathogen?
- A Naive T cells
- B Memory cells
- C Natural Killer cells
- D Macrophages
Correct answer: Memory cells
Memory B and T cells are formed during the primary immune response. They persist in the body for years and can mount a faster, stronger attack if the same pathogen enters the body again.
What is the role of 'MHC' (Major Histocompatibility Complex) proteins in the immune system?
- A To transport oxygen from the lungs to rapidly dividing immune cells
- B To act as the physical barrier that prevents pathogens from entering the skin
- C To present antigen fragments on the cell surface for T cell recognition
- D To release histamine from mast cells during an allergic reaction
Correct answer: To present antigen fragments on the cell surface for T cell recognition
MHC molecules display fragments of proteins from within the cell or captured from outside. This allows T cells to distinguish between 'self' cells and those infected by 'non-self' pathogens.
Which type of immunity is acquired by receiving a vaccine containing weakened or dead pathogens?
- A Natural passive immunity
- B Artificial passive immunity
- C Natural active immunity
- D Artificial active immunity
Correct answer: Artificial active immunity
Vaccination is considered artificial active immunity because the immune system is deliberately exposed to an antigen to trigger its own production of antibodies and memory cells.
Which cells of the immune system are primarily targeted and destroyed by the Human Immunodeficiency Virus (HIV)?
- A Helper T cells (CD4+)
- B Cytotoxic T cells (CD8+)
- C B lymphocytes
- D Neutrophils
Correct answer: Helper T cells (CD4+)
HIV infects Helper T cells, which are crucial for coordinating the entire adaptive immune response. As their numbers decline, the body becomes highly susceptible to opportunistic infections.
Large, phagocytic cells that 'crawl' through tissues to engulf debris and pathogens are called:
- A Basophils
- B Macrophages
- C Platelets
- D Red blood cells
Correct answer: Macrophages
Macrophages derive from monocytes and are essential for both innate and adaptive immunity. They act as scavengers and also function as professional antigen-presenting cells.
Which antibody class is found primarily in secretions such as saliva, tears, and breast milk?
- A IgD
- B IgM
- C IgA
- D IgE
Correct answer: IgA
IgA is the predominant antibody in mucosal secretions. It prevents pathogens from adhering to and penetrating epithelial surfaces, acting as a critical barrier defense.
Which chemical is released by mast cells and basophils, leading to vasodilation and increased capillary permeability during an allergic reaction?
- A Interferon
- B Histamine
- C Perforin
- D Complement
Correct answer: Histamine
Histamine is a key mediator of the inflammatory response. It causes the redness, swelling, and itching associated with allergies and helps recruit other immune cells to the area.
What is the function of 'Cytotoxic T cells'?
- A To produce large quantities of antibodies
- B To suppress the entire immune system after an infection
- C To directly kill infected or cancerous 'self' cells
- D To produce mucus in the respiratory tract
Correct answer: To directly kill infected or cancerous 'self' cells
Cytotoxic T cells (CD8+) recognize specific antigens presented by MHC I molecules. They release proteins like perforins and granzymes to induce apoptosis in targeted cells.
An autoimmune disease occurs when:
- A The immune system fails to respond to any pathogen
- B The immune system attacks the body's own tissues
- C There is an overproduction of red blood cells
- D The body is infected by a dormant virus
Correct answer: The immune system attacks the body's own tissues
Autoimmunity involves a breakdown of self-tolerance. The immune system mistakenly identifies the body's own proteins as foreign, leading to chronic inflammation and tissue damage.
Which immune system component consists of a group of about 30 plasma proteins that assist antibodies and phagocytes in destroying bacteria?
- A The Complement System
- B The Lymphatic System
- C The Endocrine System
- D The Integumentary System
Correct answer: The Complement System
The complement system enhances (complements) the ability of antibodies and phagocytic cells to clear pathogens. It can directly kill bacteria by forming a Membrane Attack Complex (MAC).
Natural Killer (NK) cells are unique because they:
- A Kill virus-infected and tumor cells without prior sensitization
- B Must first be activated by B cells before they can function
- C Are found in the digestive tract lining rather than in blood
- D Recognize antigens only when they are presented by MHC class II molecules
Correct answer: Kill virus-infected and tumor cells without prior sensitization
NK cells are part of the innate immune system. Unlike T cells, they do not require antigen-specific activation, allowing them to provide a rapid response to abnormal cells.
The process by which an immune cell engulfs and digests a foreign particle is called:
- A Pinocytosis
- B Exocytosis
- C Phagocytosis
- D Opsonization
Correct answer: Phagocytosis
Phagocytosis is a specialized form of endocytosis. Cells like neutrophils and macrophages wrap their plasma membrane around a pathogen to form an internal vesicle for digestion.
Which of the following describes 'passive immunity'?
- A Immunity that develops naturally after recovering from an infection
- B Immunity that the body develops after receiving a vaccination
- C The transfer of ready-made antibodies from another individual
- D The body's own production of memory T cells after exposure
Correct answer: The transfer of ready-made antibodies from another individual
Passive immunity provides immediate but short-term protection. It occurs naturally (maternal antibodies) or artificially (injection of antiserum) and does not involve the recipient's own immune system creating memory.
Which organ filters the blood, removing old red blood cells and housing various immune cells to fight blood-borne pathogens?
- A Thymus
- B Spleen
- C Thyroid
- D Gallbladder
Correct answer: Spleen
The spleen acts as a blood filter. Its white pulp contains lymphocytes that monitor the blood for pathogens, while its red pulp removes damaged or aged erythrocytes.
Interferons are signaling proteins most commonly produced by cells in response to which type of infection?
- A Bacterial
- B Prion
- C Viral
- D Parasitic
Correct answer: Viral
Interferons are cytokines released by virus-infected cells. They 'interfere' with viral replication by signaling neighboring healthy cells to trigger antiviral defenses.