Q.What is innate immunity?
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Non-Specific (Innate) Immunity — Barriers and Lines of Defence
Non-specific, or innate, immunity is the immune system's general-purpose, always-ready defence. It does not need to recognise a specific pathogen in advance, and it is traditionally described as acting in two lines, built on a broader set of four kinds of barrier.
The first line of defence consists of external barriers that try to stop a pathogen from ever entering the body at all — the skin, mucus lining the respiratory and digestive tracts (which traps particles before they can penetrate deeper), and secretions such as saliva and tears, which contain the enzyme lysozyme that breaks down bacterial cell walls.
The second line of defence comes into play once a pathogen has actually breached the first line: phagocytic cells that engulf the invader, natural killer (NK) cells that destroy infected or abnormal cells, the inflammatory response (localised redness, heat, swelling and pain as blood vessels dilate and immune cells are recruited to the site), and fever (a body-wide rise in temperature that makes conditions less favourable for many pathogens and speeds up immune cell activity). …
This form of immunity does not target any one specific pathogen and does not require prior exposure, relying instead on a fixed set of general-purpose barriers present from birth. …
Innate immunity is the non-specific defence system present in the body since birth, acting through four types of barriers to prevent entry and establishment of pathogens.
Innate (non-specific) immunity is the immunity that an individual possesses right from the time of birth. It does not involve recognition of a specific pathogen and does not improve with repeated exposure (unlike acquired/specific immunity, which is mediated by lymphocytes and 'remembers' a pathogen).
Innate immunity operates through four types of barriers:
- Physical barriers - the skin (the most important barrier, preventing microbial entry) and mucus coating of the epithelial lining of the respiratory, gastrointestinal and urogenital tracts, which traps invading microbes.
- Physiological barriers - body secretions that prevent microbial growth, e.g. acid in the stomach, saliva in the mouth, tears from the eyes.
- Cellular barriers - certain white blood cells (neutrophils, monocytes/macrophages) and natural killer (NK) lymphocytes in the blood, which engulf and destroy microbes by phagocytosis. …
Showing the 12 most recent of 20 on this concept.
- CBSE 2026Set A1 markMCQQ.What kind of barrier is the interferon secreted by virus infected cells?(a) Cytokine barrier(b) Physical barrier(c) Cellular barrier(d) Physiological barrier
›Reveal solutionSolution
Interferons are proteins (cytokines) released by virus-infected cells, forming the cytokine barrier of innate immunity.
Innate immunity has four kinds of barriers: physical (skin, mucus), physiological (acid in stomach, saliva, tears), cellular (phagocytes like macrophages, neutrophils) and cytokine barriers. Virus-infected cells secrete proteins called interferons, which protect n …
- CBSE 2025Set ANNUAL1 markMCQQ.Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection is called(a) cellular barrier(b) physiological barrier(c) physical barrier(d) cytokine barrier
›Reveal solutionSolution
Interferons are the classic example of the cytokine barrier component of innate immunity.
Innate immunity provides four types of barriers: physical (skin, mucus), physiological (stomach acid, saliva, tears), cellular (phagocytic cells, NK cells), and cytokine barriers. When a cell is infected by a virus, it secretes small signalling proteins called interferons. These interferons diffuse to and act on neighbouring, still-uninfected cells, inducing in them an "antiviral state" that protects them from being infected by the same virus. This mechanism — protection of surrou …
- CBSE 2025Set ANNUAL1 markMCQQ.A cytokine barrier, which is an innate immunity, depends on the production of certain substance by an infected cells that protects other cells from further infection. Identify this substance -(i) Histamine(ii) Serotonin(iii) Interferon(iv) Phagocyte
›Reveal solutionSolution
Virus-infected cells secrete interferons, which protect neighbouring, still-uninfected cells from being infected by the same virus — this is the cytokine barrier of innate immunity.
Innate immunity includes several types of physiological/cellular barriers, one of which is the cytokine barrier. When a cell is infected by a virus, it secretes proteins called interferons. These interferons diffuse to and act on nearby uninfected cells, inducing an antiviral state in them (by interfering with viral replication machinery), so that even if these neighbouring cells subsequently get exposed to the virus, they are protected from further infection.
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- CBSE 2024Set 57/2/11 markMCQQ.Assertion (A) : Virus-infected cells produce interferons. Reason (R) : Interferons can cause inflammation of virus-infected cells. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.
›Reveal solutionSolution
Assertion (A) is true because virus-infected cells produce interferons as an antiviral defense. Reason (R) is false because interferons primarily induce an antiviral state in neighboring cells and activate immune cells, rather than directly causing inflammation of the infected cells themselves. The correct option is (C).
Concept and Intuition
Our bodies have a sophisticated defense system against pathogens like viruses. When a cell gets infected by a virus, it's not a passive victim; it actively tries to alert its neighbors and the broader immune system. One crucial way it does this is by producing signaling molecules called interferons.
Interferons are a type of cytokine (cell-signaling protein) that play a vital role in the innate immune response, particularly against viral infections. Their primary function is to "interfere" with viral replication. They achieve this mainly by:
- Signaling to uninfected cells: Interferons bind to receptors on nearby healthy cells, prompting them to produce antiviral proteins. These proteins can then block viral replication if those cells become infected. This is like putting up a protective shield around healthy cells.
- Activating immune cells: Interferons also activate various immune cells, such as Natural Killer (NK) cells and macrophages, which are crucial for destroying virus-infected cells and clearing the infection.
- Modulating immune responses: They can also influence the adaptive immune system.
Inflammation, on the other hand, is a complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. It's characterized by redness, swelling, heat, pain, and loss of function. While interferons are part of the broader immune response that can contribute to inflammation by activating immune cells, their direct action is not to cause inflammation of the virus-infected cells themselves. Instead, they focus on protecting uninfected cells and orchestrating the elimination of infected ones.
Step-by-Step Evaluation
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Evaluate Assertion (A): "Virus-infected cells produce interferons."
- When a virus infects a cell, the cell recognizes viral components (like viral RNA or DNA). This recognition triggers a signaling pathway within the infected cell, leading to the production and secretion of interferons (specifically Type I interferons, such as IFN-alpha and IFN-beta). These interferons are then released into the extracellular space.
- This statement accurately describes a fundamental aspect of the innate antiviral immune response.
- Therefore, Assertion (A) is true.
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Evaluate Reason (R): "Interferons can cause inflammation of virus-infected cells."
- As discussed, the primary role of interferons is to induce an antiviral state in neighboring uninfected cells and to activate other immune cells to clear the infection. They do not directly cause inflammation of the virus-infected cells. …
- CBSE 2024Set E1 markMCQQ.Which of the following blood cells is known as PMNL?(a) Lymphocyte(b) Monocyte(c) Neutrophil(d) Platelets
›Reveal solutionSolution
Neutrophils are the polymorphonuclear leukocytes (PMNL), named for their many-lobed nucleus.
White blood cells are grouped by nuclear shape:
- Neutrophils have a nucleus with several (poly-) lobes, so they are called POLYMORPHONUCLEAR leukocytes (PMNL). They are phagocytic cells of the innate immune system and are the most abundant WBC. …
- CBSE 2024Set D1 markQ.Write True or False: Each interferon has its own speciality.
›Reveal solutionSolution
The statement is True — interferons are not a single uniform substance; each type has its own distinctive characteristics.
Interferons are proteins secreted by virus-infected cells as part of the innate/non-specific immune response. They diffuse to and bind to neighbouring, uninfected cells, inducing those cells to produce substances (antiviral proteins) that inhibit viral replication, thereby protecting them from further infection.
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- CBSE 2024Set D1 markQ.Answer in one sentence: How do cytokine barriers provide innate immunity in humans?
›Reveal solutionSolution
Cytokine barriers involve virus-infected cells secreting interferons that protect nearby, uninfected cells from being infected by the same virus.
Innate immunity is the non-specific type of defence present in the body from birth, and it operates through four types of barriers: physical barriers (e.g., skin, mucus lining), physiological barriers (e.g., acid in the stomach, saliva, tears), cellular barriers (e.g., phagocytes, natural killer cells), and cytokine barriers.
The cytokine barrier specifically refers to the action of interferons — small proteins secreted by cells that have been infected by a virus. Once released, interferons diffuse out and bind to receptors on nearby, still-healthy (uninfected) cells.
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- CBSE 2024Set ANNUAL1 markMCQQ.Virus-infected cells secrete proteins called ................ which protect non-infected cells from further viral infection.(a) exon(b) intron(c) interferon(d) neutrophils
›Reveal solutionSolution
When a cell is infected by a virus, it secretes interferons, small proteins that alert and protect nearby healthy cells from getting infected.
Interferons are part of the body's innate, non-specific antiviral defence. A virus-infected cell releases interferons which diffuse to neighbouring cells and induce them to produce antiviral proteins that interfere with viral replication - so even if the virus reaches those cells, its multiplication is blocked. Exons and introns are …
- CBSE 2024Set ANNUAL1 markMCQQ.Assertion (A) : Interferons are a type of antibodies produced by bacteria infected cells of the body. Reason (R) : Interferons stimulate inflammation at the site of injury.(a) Assertion (A) and Reason (R) both are true and Reason (R) is the correct explanation of Assertion (A).(b) Assertion (A) and Reason (R) both are true, but Reason (R) is not the correct explanation of Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) and Reason (R) both are false.
›Reveal solutionSolution
Interferons are not antibodies, and their chief role is antiviral protection of neighbouring cells, not stimulating inflammation.
Interferons are a special class of proteins secreted by virus-infected cells (not merely bacteria-infected cells) as part of the innate/cell-mediated defence response — they are NOT antibodies, which are a distinct class of proteins (immunoglobulins) produced by plasma cells (B-lymphocytes) as part of humoral/specific immunity. So the Assertion is false. Interferons' principal function is to protect uninfected neighbo …
- CBSE 2024Set ANNUAL1 markMCQQ.The protein which is secreted by virus-infected cells to protect non-infected cells is called(a) antigen(b) antibody(c) antibiotic(d) interferon
›Reveal solutionSolution
Interferons are antiviral proteins secreted by virus-infected cells that help neighbouring healthy cells resist infection.
When a cell is infected by a virus, it can secrete small signalling proteins called interferons, which diffuse to neighbouring, still-uninfected cells and induce in them an antiviral state (by activating enzymes that interfere with viral replication), protecting them against infection by the same or related viruses. Antigens (a) are the foreign molecules that trigge …
- CBSE 2024Set ANNUAL1 markQ.Virus infected cells provide innate immunity to other uninfected cells. Analyse.
›Reveal solutionSolution
Interferons secreted by virus-infected cells alert and protect surrounding healthy cells, providing a rapid, non-specific innate immune defence against the spread of viral infection.
When a cell is infected by a virus, it produces and secretes a class of proteins called interferons. These are released into the surrounding tissue and bind to receptors on neighbouring, uninfected cells, inducing an antiviral state in them — such cells produce proteins/enzymes that interfere with viral replication (e.g., by degrading viral RNA or inhibiting protein synthesis), so that even if they are subsequently exposed to the virus, infection and replication are blocked or greatly reduced. This response is rapid, occurs without recognising a speci …
- CBSE 2024Set ANNUAL1 markQ.State the examples of physical barriers in innate immunity
›Reveal solutionSolution
Skin and mucus-secreting epithelial linings act as the body's first-line physical barriers against pathogen entry.
Innate immunity is a non-specific type of defence present from birth, made up of four types of barriers — physical, physiological, cellular and cytokine barriers. The physical barriers prevent entry of micro-organisms into the body and include:
- The skin, which forms the outermost, mechanically tough covering of the body, preventing entry of most pathogens. …
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