Immunity Questions in English

(D) Interferons are a group of signaling proteins made and released by host cells in response to the presence of several viruses.
When a cell is infected by a virus,it produces interferons to protect neighboring healthy cells from viral infection.
Therefore,virus-infected cells are responsible for the secretion of interferons.

(C) An antibody molecule has a structure represented as $H_2L_2$,consisting of two heavy $(H)$ chains and two light $(L)$ chains.
Each antibody molecule has two antigen-binding sites,known as paratopes.
Each paratope is formed by the variable regions of one heavy chain and one light chain,which come together to create a specific binding pocket for the antigen.

(D) -lymphocytes are a type of white blood cell that plays a crucial role in the humoral immune response.
When pathogens (like bacteria or viruses) enter the body,$B$-lymphocytes recognize them and differentiate into plasma cells.
These plasma cells secrete specialized proteins known as antibodies (immunoglobulins) into the blood and lymph.
These antibodies specifically bind to the antigens on the surface of the pathogens,neutralizing them or marking them for destruction by other immune cells.

(A) Cellular barriers are a component of innate immunity that prevents the entry of microbes into the body.
These barriers include certain types of leukocytes (white blood cells) that can phagocytose and destroy microbes.
Specifically,polymorphonuclear leukocytes (PMNLs) or $Neutrophils$ and $Monocytes$ (which differentiate into $Macrophages$ in tissues) are the primary cells involved in phagocytosis within the cellular barrier system.
Therefore,the pair of white blood cells involved in cellular barriers is $Neutrophils$ and $Monocytes$.

(B) Antibodies,also known as immunoglobulins $(Ig)$,are glycoproteins produced by plasma cells in response to antigens.
There are five main classes of antibodies in humans: $IgA$,$IgD$,$IgE$,$IgG$,and $IgM$.
$IgB$ is not a recognized class of antibody in human immunology.
Therefore,$IgB$ is the correct answer.

(B) Innate immunity is a non-specific type of defense that is present at the time of birth. It provides resistance against pathogens upon their first entry into the body. It consists of various barriers like physical,physiological,cellular,and cytokine barriers that prevent the entry or growth of foreign agents. Therefore,option $B$ is the most accurate description of its function.

(A) Acquired immunity is pathogen-specific and is characterized by memory. When the body encounters a pathogen for the first time,it produces a primary response of low intensity. Subsequent encounters with the same pathogen elicit a highly intensified secondary or anamnestic response. This secondary response is due to the memory of the first encounter,which is a fundamental characteristic of acquired immunity. Therefore,$R$ correctly explains $A$.

(B) Immunity is broadly classified into two types: Innate and Acquired.
$1$. Innate immunity is present at the time of birth and is non-specific.
$2$. Acquired immunity is pathogen-specific and is developed by an organism during its lifetime after birth.
Therefore,the immunity developed during a lifetime is known as Acquired immunity.

(D) When a pathogen enters the body,the immune system responds by producing antibodies. This specific type of acquired immunity,which is mediated by antibodies present in the blood and lymph,is known as $Humoral$ $immunity$ or $Antibody-mediated$ $immunity$ $(AMI)$. In contrast,$Cell-mediated$ $immunity$ $(CMI)$ is mediated by $T-lymphocytes$ and does not involve antibodies.

(B) Antibodies are specialized proteins produced by $B$-lymphocytes in response to pathogens. These are also known as immunoglobulins $(Ig)$.
There are five main classes of antibodies found in the human body: $IgA$,$IgM$,$IgE$,$IgG$,and $IgD$.
Option $B$ contains three of these valid classes $(IgM, IgE, IgG)$,whereas the other options contain non-existent classes like $IgB, IgC,$ or $IgF$.

(A) Innate immunity consists of four types of barriers: physical,physiological,cellular,and cytokine barriers.
Cellular barriers include cells like polymorphonuclear leukocytes ($PMNL$-neutrophils),monocytes,and natural killer cells in the blood,as well as macrophages in tissues.
These cells phagocytose and destroy microbes.
Therefore,$PMNL$ is the correct representation of cellular barriers.

(C) An antibody molecule is a $Y$-shaped structure composed of four polypeptide chains.
These include two identical light chains ($L$-chains) and two identical heavy chains ($H$-chains).
These chains are held together by disulfide bonds.
Therefore,the correct answer is polypeptide chains.

(A) Immunity is defined as the overall ability of the host to fight the disease-causing organisms conferred by the immune system. While options $B$,$C$,and $D$ describe specific functions or mechanisms of the immune system,option $A$ provides the most comprehensive definition of immunity as the collective capacity to defend against pathogens.

(B) Each antibody molecule consists of four polypeptide chains.
There are two small chains called light chains $(L)$ and two longer chains called heavy chains $(H)$.
These chains are held together by disulfide bonds to form a $Y$-shaped structure.
Therefore,an antibody molecule is represented as $H_2L_2$.

(B) In the human immune system,$B$-lymphocytes (or $B$-cells) are responsible for producing antibodies. However,this process is not independent. $T$-helper cells ($CD4^+$ cells) recognize antigens presented by $B$-cells and release cytokines that stimulate $B$-cells to proliferate and differentiate into plasma cells,which then secrete antibodies. Therefore,$T$-cells play a crucial role in assisting $B$-cells in the production of antibodies.

(A) An antibody molecule is composed of four polypeptide chains: two identical light $(L)$ chains and two identical heavy $(H)$ chains,represented as $H_2L_2$.
These chains are held together by disulfide bonds ($S-S$ bonds) to form a $Y$-shaped structure.
Therefore,the correct answer is disulfide bonds.

(A) Interferons $(IFNs)$ are a group of signaling proteins made and released by host cells in response to the presence of several viruses. They act as a type of cytokine. When a cell is infected by a virus,it secretes interferons,which signal neighboring non-infected cells to heighten their antiviral defenses,thereby protecting them from infection.

(A) An antibody molecule is represented by the formula $H_2L_2$.
This means it consists of four polypeptide chains: two identical light chains $(L)$ and two identical heavy chains $(H)$.
These chains are held together by disulfide bonds to form a $Y$-shaped structure.
Therefore,each antibody molecule contains two heavy polypeptide chains.

(A) Antibodies are produced by $B$-lymphocytes (or $B$-cells) in response to pathogens.
When $B$-cells encounter an antigen,they differentiate into plasma cells,which then secrete large quantities of antibodies into the blood and lymph.
$T$-cells,on the other hand,do not produce antibodies directly but help $B$-cells in the immune response.

(B) Interferons are proteins secreted by virus-infected cells which protect non-infected cells from further viral infection.
These proteins act as a chemical messenger system that triggers the antiviral state in neighboring cells.
In the context of innate immunity,barriers are classified as:
$1$. Physical barriers (e.g.,skin,mucus coating).
$2$. Physiological barriers (e.g.,acid in the stomach,saliva in the mouth,tears from eyes).
$3$. Cellular barriers (e.g.,leukocytes like $PMNL$-neutrophils,monocytes,and natural killer cells).
$4$. Cytokine barriers (e.g.,interferons).
Therefore,interferons are categorized under cytokine barriers.

(B) Phagocytosis is a process by which cells engulf and destroy pathogens or cellular debris.
In the human immune system,the primary phagocytic cells are Monocytes,Macrophages,and Polymorphonuclear Leukocytes ($PMNL$ or Neutrophils).
Natural Killer $(NK)$ cells are cytotoxic lymphocytes that destroy infected or cancerous cells but are not primarily phagocytic.
Lymphocytes ($B$ and $T$ cells) are involved in specific immune responses and are not phagocytic.
Therefore,the group consisting of Monocytes,Macrophages,and $PMNL$ represents the phagocytic cells.

(B) An antigen is a foreign molecule or substance,such as proteins,polysaccharides,or toxins,that enters the body and is recognized by the immune system as 'non-self'. Upon recognition,the immune system is stimulated to produce specific proteins called antibodies to neutralize or eliminate the antigen. Therefore,option $B$ is the correct definition.

(B) An $Antigen$ is a molecule or molecular structure, such as may be present at the outside of a pathogen, that can be bound by an antigen-specific antibody or $B$-cell antigen receptor. The presence of antigens in the body triggers the immune system to produce antibodies, thereby initiating an immune response. Therefore, the correct option is $B$.

(C) When a pathogen or a foreign substance (antigen) enters the host body,the immune system recognizes it as non-self.
In response to this,the $B$-lymphocytes are activated and differentiate into plasma cells.
These plasma cells produce specialized proteins called antibodies (immunoglobulins) to neutralize or eliminate the foreign agent.
Therefore,the substance produced by the host in response to an infection or foreign body is an antibody.

(D) Antibodies are specialized proteins produced by the immune system to identify and neutralize foreign objects like bacteria and viruses.
In the human body,$B$-lymphocytes are the specific type of white blood cells responsible for the production of antibodies.
When $B$-lymphocytes encounter an antigen,they differentiate into plasma cells,which then secrete large quantities of antibodies into the blood and lymph.
Therefore,the correct answer is $D$ (Lymphocytes).

(D) Active immunity is developed when an individual's own immune system produces antibodies in response to antigens (like pathogens or vaccines). It is long-lasting.
Passive immunity is acquired when ready-made antibodies are directly introduced into the body (e.g.,through colostrum or injections). Since the individual's own immune system does not produce these antibodies,it provides immediate but temporary protection.

(D) Passive immunity is defined as the transfer of active humoral immunity in the form of ready-made antibodies from one individual to another.
In the case of a newborn infant,the mother transfers antibodies,specifically $IgA$ through colostrum (the yellowish fluid produced during initial days of lactation) and $IgG$ through the placenta during pregnancy.
This provides immediate protection to the infant against various pathogens,which is why it is termed passive acquired immunity.

(B) Acquired immunity is pathogen-specific and is characterized by memory.
When the body encounters a pathogen for the first time,it produces a primary response of low intensity.
Subsequent encounters with the same pathogen elicit a highly intensified secondary or anamnestic response.
Active acquired immunity involves the activation of the immune system to produce antibodies in response to antigens,which is a time-consuming process.
Passive acquired immunity involves the direct transfer of ready-made antibodies,but the question specifically refers to the nature of the immune response development,which is characteristic of active acquired immunity.

(A) Passive acquired immunity is a type of immunity where pre-formed antibodies are directly injected into the body to provide immediate protection against specific pathogens or toxins.
In contrast,active immunity involves the administration of antigens (like in vaccines) which stimulate the body's immune system to produce its own antibodies.
Therefore,for passive immunity,ready-made antibodies are injected.

(B) Active immunity is developed when the host's immune system is exposed to antigens,which may be present in the form of living or dead microbes or other proteins.
When these antigens are introduced into the body,antibodies are produced in the host body in response to them.
Option $B$ describes the process of vaccination,which is a form of active immunity where dead or weakened pathogens are introduced to stimulate the immune system.
Option $A$ describes passive immunity,where pre-formed antibodies are directly injected into the body.

(D) Passive immunity is defined as the immunity acquired when ready-made antibodies are directly given to protect the body against foreign agents.
$1$. The transfer of $IgA$ antibodies from mother's milk to the newborn infant is a classic example of natural passive immunity.
$2$. The transfer of $IgG$ antibodies from the mother to the fetus through the placenta during pregnancy is also a form of natural passive immunity.
$3$. The administration of pre-formed antibodies (e.g.,anti-tetanus serum or anti-venom) directly into the body is an example of artificial passive immunity.
Since all these processes involve the transfer of pre-formed antibodies rather than the body producing its own,all of the given options are correct.

(A) Passive immunity is a type of immunity where the body does not produce its own antibodies but receives them from an external source.
In passive acquired immunity,pre-formed antibodies are directly injected into the body to provide immediate protection against specific pathogens.
This is different from active immunity,where the body's immune system is stimulated to produce its own antibodies (e.g.,through vaccination or natural infection).
Therefore,option $A$ is the correct answer.

(D) Passive immunity is a type of immunity where pre-formed antibodies are directly introduced into the body to provide immediate protection against specific pathogens or toxins.
Unlike active immunity,where the body's immune system produces its own antibodies after exposure to an antigen,passive immunity does not involve the activation of the host's immune system.
Examples include the transfer of $IgG$ antibodies from mother to fetus through the placenta and the administration of anti-tetanus serum or anti-venom injections.

(B) Passive immunity is a type of immunity where preformed antibodies are directly introduced into the body to provide immediate protection.
It does not involve the activation of the host's immune system to produce its own antibodies or memory cells.
Option $B$ is incorrect because the formation of $B$ and $T$ memory cells is a characteristic feature of active immunity,where the host's immune system is exposed to an antigen and develops a long-term response.
Options $A$,$C$,and $D$ are all examples of passive immunity: $A$ (natural passive immunity via placenta),$C$ (natural passive immunity via colostrum),and $D$ (artificial passive immunity via antitoxins).

(D) When a host is exposed to antigens (such as proteins or polysaccharides from pathogens),the immune system recognizes them as foreign.
This triggers an immune response where $B-$ lymphocytes produce specific antibodies to neutralize the antigen.
Simultaneously,$T-$ lymphocytes are activated to assist in the immune response and destroy infected cells.
Therefore,both antibodies and $T-$ cells are produced/activated in the host body in response to antigen exposure.

(D) Antigens are substances that the body recognizes as foreign and that trigger an immune response. They can exist in various forms,including:
$1$. Living microorganisms (e.g.,pathogens like bacteria or viruses).
$2$. Dead or inactivated microorganisms (often used in vaccines).
$3$. Other proteins or molecules (such as pollen,toxins,or foreign blood cells).
Therefore,all the given options are valid forms in which antigens can exist.

(B) When a host is exposed to antigens,which may be in the form of living or dead microbes or other proteins,antibodies are produced in the host body. This type of immunity is called active immunity. It is slow and takes time to give its full effective response. Therefore,it is known as active acquired immunity.

(A) The process of intentionally introducing weakened or inactivated microorganisms (or their antigens) into the body to stimulate an immune response is known as vaccination or immunization.
This process triggers the immune system to produce antibodies and memory cells against the specific pathogen.
Since the body's own immune system actively produces these antibodies in response to the antigen,this is classified as $Active$ $Acquired$ $Immunity$.
In contrast,$Passive$ $Immunity$ involves the direct transfer of pre-formed antibodies (e.g.,through the placenta or colostrum),where the recipient's immune system does not actively participate.

(C) When pre-formed antibodies are directly injected into the body to provide immediate protection against antigens (such as in the case of tetanus or snake bites), it is known as $Passive$ $acquired$ $immunity$.
In this type of immunity, the body does not produce antibodies itself, but receives them from an external source.
Therefore, the correct option is $C$.

(B) Mother's milk,especially the initial yellowish fluid secreted during the first few days of lactation,is called colostrum.
Colostrum contains abundant antibodies,specifically $IgA$,which are essential to develop resistance for the newborn baby.
This provides passive immunity to the infant,protecting them from various infections during their early development.

(A) Active immunity is defined as the immunity developed by an individual's own immune system in response to the presence of antigens (such as pathogens or vaccines).
When a host is exposed to antigens,which may be in the form of living or dead microbes or other proteins,the immune system produces antibodies in the host body.
This process is slow and takes time to give its full effective response.
In contrast,passive immunity involves the direct introduction of pre-formed antibodies into the body,and innate immunity is the immunity present from birth.

(C) Passive acquired immunity is a type of immunity where the body does not produce its own antibodies in response to an antigen.
Instead,pre-formed or ready-made antibodies are directly introduced into the body to provide immediate protection.
Examples include the transfer of $IgG$ antibodies from mother to fetus through the placenta and $IgA$ antibodies through colostrum,or the administration of anti-tetanus serum $(ATS)$ after an injury.

(B) Passive immunity is a type of immunity where the body receives ready-made antibodies rather than producing them through its own immune system.
When a person is exposed to antigens (like in a vaccine),the body produces its own antibodies,which is called active immunity.
However,when pre-formed antibodies are directly injected into the body (e.g.,anti-tetanus serum or antibodies transferred from mother to fetus via placenta),it is known as passive immunity.
Therefore,the correct answer is ready-made antibodies.

(A) Active immunity is the type of immunity developed by an individual's own immune system when it is exposed to antigens,such as pathogens or vaccines.
When a person is exposed to an infection (pathogen),the immune system produces antibodies and memory cells to fight the disease.
This process occurs after the body encounters the antigen,making it a form of active acquired immunity.

(A) Active acquired immunity is developed when the immune system encounters an antigen and produces a specific response.
This process involves the activation of $B$-lymphocytes and $T$-lymphocytes.
Upon the first exposure to an antigen,the immune system generates memory cells.
These memory cells are responsible for recognizing the same pathogen upon subsequent exposure,leading to a faster and more intense secondary immune response.
Therefore,memory cells are the key components responsible for the long-term protection associated with active acquired immunity.

(A) When a host is exposed to antigens,which may be in the form of living or dead microbes or other proteins,antibodies are produced in the host body. This type of immunity is called active immunity.
Active immunity is slow and takes time to give its full effective response.
Infection induces active immunity as the body's immune system actively produces antibodies against the pathogen.
Therefore,immunity acquired after an infection is active immunity.

(A) When a host is exposed to antigens,which may be in the form of living or dead microbes or other proteins,antibodies are produced in the host body. This type of immunity is called active immunity.
Active immunity is slow and takes time to give its full effective response.
Recovering from a disease like smallpox or chickenpox involves the body's immune system encountering the pathogen,fighting it,and creating memory cells,which is a classic example of natural active immunity.

(A) Active acquired immunity involves the exposure of the host to antigens,which can be in the form of live or dead microbes or other proteins. When these antigens are introduced into the body,the immune system produces antibodies and generates memory cells to provide long-term protection. This is the principle behind vaccination,where infectious organisms are deliberately introduced to stimulate an immune response without causing the disease.

(D) Passive acquired immunity is a type of immunity where ready-made antibodies are directly introduced into the host body to provide immediate protection.
This is in contrast to active immunity,where the body produces its own antibodies in response to antigens.
Examples include the transfer of $IgG$ antibodies from mother to fetus through the placenta and $IgA$ antibodies through colostrum.

(A) Passive immunity is a type of immunity where pre-formed antibodies are directly introduced into the body to provide immediate protection against a pathogen.
Unlike active immunity,where the body's immune system produces its own antibodies in response to an antigen (as in vaccination or natural infection),passive immunity does not involve the activation of the host's immune system.
Examples include the transfer of $IgG$ antibodies from mother to fetus through the placenta and $IgA$ antibodies through colostrum,or the administration of anti-venom injections.