Immunity Questions in English

(A) Interferons were first discovered in $1957$ by Alick Isaacs and Jean Lindenmann. They observed that cells infected with the $Influenza$ virus produced a substance that interfered with the replication of other viruses in neighboring cells. This substance was named 'interferon'.

(B) Interferons are a group of signaling proteins made and released by host cells in response to the presence of several pathogens,such as viruses. When a cell is infected by a virus,it secretes interferons,which signal neighboring cells to heighten their anti-viral defenses. Thus,interferons specifically inhibit viral replication.

(B) $Interferon$ is a low molecular weight antiviral protein produced by host cells in response to viral infection. It inhibits viral multiplication and protects neighboring cells against further viral infection.

(A) Interferons are a group of signaling proteins made and released by host cells in response to the presence of several viruses.
They act as a part of the innate immune system.
When a cell is infected by a virus,it secretes interferons,which signal neighboring cells to heighten their anti-viral defenses.
Therefore,interferons are produced in response to viral infections to prevent further replication of the virus within the host.

(D) When a horse is injected with cobra venom,its immune system produces specific antibodies against the venom.
This serum,containing pre-formed antibodies,is then extracted and injected into a person bitten by a cobra.
Since the person receives ready-made antibodies rather than their own immune system producing them,this is known as $Passive \ immunity$.
This method provides immediate protection against the toxin.

(B) Lymph nodes are secondary lymphoid organs that act as filters for the lymph fluid. They trap microorganisms,such as bacteria and viruses (germs),that enter the lymph and tissue fluid. Within the lymph nodes,lymphocytes (a type of $W.B.C.$) are activated to mount an immune response against these pathogens. Therefore,lymph nodes play a crucial role in fighting against germs.

(D) . Neutrophils,macrophages,and lymphocytes are all integral components of the immune system.
Neutrophils and macrophages act as phagocytes that engulf and destroy foreign pathogens.
Lymphocytes are responsible for the specific immune response,including the production of antibodies and the destruction of infected cells.

(A) Antibodies are specialized proteins produced by a specific sub-population of white blood cells known as $B$-lymphocytes.
When $B$-lymphocytes encounter an antigen,they differentiate into plasma cells,which then secrete large quantities of antibodies into the blood and lymph to neutralize the pathogen.
$T$-lymphocytes,on the other hand,do not produce antibodies directly but help $B$-lymphocytes in the immune response.

(D) An antibody,also known as an immunoglobulin $(Ig)$,is a large,$Y$-shaped protein produced by plasma cells (differentiated $B$-lymphocytes).
Its primary function is to identify and neutralize foreign objects such as bacteria and viruses.
Antibodies recognize and bind to specific antigens,which are unique molecules on the surface of pathogens,thereby inactivating them or marking them for destruction by other components of the immune system.

(B) Antiserum is a blood serum containing polyclonal antibodies that are used to pass on passive immunity to many diseases. It is prepared by injecting an antigen into an animal or human,which then produces specific antibodies against that antigen. Therefore,antiserum contains antibodies for a specific antigen.

(C) Peyer's patches are organized lymphoid follicles found in the submucosa of the small intestine,particularly in the ileum.
These structures are part of the gut-associated lymphoid tissue $(GALT)$.
They play a crucial role in the immune system by monitoring intestinal bacteria populations and preventing the growth of pathogenic bacteria.
They are primarily composed of aggregates of lymphocytes,which are white blood cells responsible for the immune response.

(A) Lymphocytes are a type of white blood cell $(WBC)$ that play a crucial role in the immune system.
They are responsible for identifying and destroying foreign invaders such as bacteria,viruses,and other pathogens.
Therefore,lymphocytes protect the body from pathogens.

(A) Antibodies are specialized proteins produced by the immune system,specifically by $B$-lymphocytes (plasma cells),in response to the presence of antigens such as bacteria,viruses,or other pathogens.
Their primary function is to identify,neutralize,and help eliminate these foreign invaders from the body,thereby protecting the host against infections.
Thirst,starvation,and heart failure are physiological or pathological conditions that are not directly countered by the production of antibodies.

(A) An antibody,also known as an immunoglobulin $(Ig)$,is a protective protein produced by the immune system in response to the presence of a foreign substance called an antigen.
Antibodies are highly specific; they recognize and bind to specific antigens to neutralize them or mark them for destruction by other immune cells.
Therefore,an antibody is a molecule that specifically inactivates an antigen.

(A) Antibodies are specialized proteins known as immunoglobulins $(Ig)$.
They are produced by plasma cells,which are differentiated $B$-lymphocytes.
$B$-lymphocytes originate and mature in the bone marrow.
Therefore,the primary site for the formation of these cells and the subsequent production of antibodies is the bone marrow.

(B) $T$-lymphocytes and $B$-lymphocytes originate from haemopoietic stem cells located in the bone marrow.
After their initial formation in the bone marrow,$T$-lymphocytes migrate to the thymus gland,where they undergo maturation and proliferation.
Therefore,the site of origin for $T$-lymphocytes is the bone marrow.

(D) The correct answer is $(d)$. Lymph nodes,spleen,thymus,and tonsils are secondary lymphoid organs that produce lymphocytes. These lymphocytes produce antibodies that destroy bacteria,foreign cells,and viruses that invade the body.

(C) 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.
Antigens are recognized by the immune system as foreign substances.
When the immune system detects an antigen,it triggers the production of specific antibodies to neutralize or eliminate the pathogen.
Therefore,an antigen acts as a stimulus for antibody production.

(D) Antibodies are specialized proteins known as immunoglobulins $(Ig)$.
They are produced by specialized white blood cells called $B$-lymphocytes (or $B$-cells).
These $B$-lymphocytes mature and reside within the lymphoid tissues,such as the spleen,lymph nodes,and tonsils,where they differentiate into plasma cells to secrete antibodies in response to antigens.
Therefore,the correct answer is lymphoid tissue.

(A) Antibodies $(Ig)$ are specialized proteins produced by $B$-lymphocytes in response to pathogens.
When an antibody encounters an antigen,it binds specifically to the antigen's epitope to form an antigen-antibody complex.
This binding neutralizes the antigen by blocking its active sites,preventing it from attaching to host cells,and restricting its mobility,which effectively inhibits its ability to cause damage to the body.

(D) Humoral immunity,also known as antibody-mediated immunity,involves the production of specialized proteins called antibodies.
These antibodies are synthesized and secreted by plasma cells,which are the differentiated form of activated $B$-lymphocytes.
Once produced,these antibodies circulate in the blood plasma and lymph,where they identify and neutralize pathogens like bacteria and viruses.

(C) Lymphocytes are a type of white blood cell that play a crucial role in the immune system.
They are primarily responsible for the adaptive immune response.
When the body encounters a pathogen,$B$-lymphocytes differentiate into plasma cells,which produce specialized proteins called antibodies or immunoglobulins.
These immunoglobulins recognize and neutralize specific antigens,thereby providing the principal defence mechanism for the body.

(D) Lymph nodes are secondary lymphoid organs that act as filters for the lymph fluid. They trap microorganisms or other antigens that enter the lymph and tissue fluid. Within the lymph nodes,lymphocytes are activated and differentiate into plasma cells,which then produce antibodies to fight the infection.

(D) Lymphoid tissues are the organs and tissues where origin,maturation,and proliferation of lymphocytes occur.
$1.$ The primary lymphoid organs are the bone marrow and thymus,where immature lymphocytes differentiate into antigen-sensitive lymphocytes.
$2.$ Secondary lymphoid organs,such as the spleen,lymph nodes,tonsils,Peyer's patches of the small intestine,and the appendix,provide the sites for interaction of lymphocytes with the antigen.
Therefore,all the given options contain lymphoid tissue.

(C) The transplantation of tissue or organs between individuals of different species is known as a $Xenograft$.
$Autograft$ refers to tissue transplanted from one site to another on the same individual.
$Isograft$ refers to a transplant between genetically identical individuals (e.g.,identical twins).
$Allograft$ refers to a transplant between individuals of the same species but with different genetic makeups.

(C) $IgG$ is the most abundant antibody in the human body,accounting for approximately $80\%$ of the total serum antibodies.
It is the only class of antibody capable of crossing the placenta from the mother to the fetus,providing passive immunity to the newborn.

(C) The correct answer is $(c)$ Isograft.
An Isograft (also known as a syngeneic graft) is a tissue transplant between two genetically identical individuals,such as identical twins.
Since their genetic makeup is identical,the immune system of the recipient does not recognize the graft as foreign,minimizing the risk of rejection.

(C) 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 communication signal between cells to trigger the protective defenses of the immune system that eradicate pathogens.
Interferons are low molecular weight proteins that prevent further viral replication in neighboring healthy cells,thereby providing innate immunity against viral infections.

(C) The 'first line of defence' in the human body consists of physical and physiological barriers that prevent the entry of pathogens.
Skin is the primary physical barrier that acts as the first line of defence by preventing the entry of microorganisms into the body.
Other components like mucus and secretions also contribute to this barrier,but among the given options,skin is the correct answer.

(B) The human body has three lines of defence against pathogens.
$1$. The 'first line of defence' consists of physical and physiological barriers like skin,mucus,and secretions.
$2$. The 'second line of defence' is the innate immune response,which includes cellular barriers like $WBC$ (specifically phagocytes like macrophages and neutrophils),inflammatory responses,and fever.
$3$. The 'third line of defence' is the adaptive or acquired immune response,which involves $B$-lymphocytes and $T$-lymphocytes (antibodies).
Therefore,$WBC$ are the components that constitute the second line of defence.

(D) The overall ability of the host to fight the disease-causing organisms,conferred by the immune system,is called $Immunity$.
It involves various mechanisms that protect the body from pathogens,toxins,and other foreign substances.
Therefore,the correct term for the body's defence mechanism against diseases is $Immunity$.

(D) Vaccines work on the principle of immunological memory. When a vaccine is introduced into the body,it contains inactivated or weakened pathogens (antigens). The immune system recognizes these antigens as foreign and initiates an immune response. This process leads to the production of specific $Antibodies$ and the formation of memory $B$-cells and $T$-cells. These memory cells are stored in the body,allowing for a rapid and robust response if the actual pathogen infects the individual in the future.

(C) $Booster$ $dose$ is an extra administration of a vaccine after an earlier (prime) dose.
It is given to increase the immunity back to protective levels after memory against that antigen has declined over time.
Therefore,the correct term for the additional dose given to maintain immunization is the $Booster$ $dose$.

(C) Antigens are foreign substances,such as proteins,polysaccharides,or toxins,that enter the body and are recognized by the immune system as non-self.
When these substances enter the body,they stimulate the immune system to produce specific antibodies to neutralize or eliminate them.
Therefore,the substances that trigger an immune response are known as antigens.

(D) The immune system of the human body consists of $B$-lymphocytes ($B$-cells) and $T$-lymphocytes ($T$-cells),which are responsible for humoral and cell-mediated immunity,respectively.
When there is a deficiency or complete absence of these functional cells,the body cannot mount an effective immune response against pathogens.
This condition,characterized by the failure of the immune system to function properly,is known as immune deficiency.

(D) -lymphocytes are a type of white blood cell that plays a crucial role in the adaptive immune system.
They are responsible for mediating humoral immunity by differentiating into plasma cells that secrete antibodies.
In humans,$B$-cells are produced and mature in the bone marrow.
In contrast,$T$-cells are produced in the bone marrow but migrate to the thymus for maturation.

(D) Suppressor $T$-cells are a specialized sub-population of $T$-lymphocytes.
Their primary function is to regulate the immune response by suppressing the activity of other immune cells,such as Helper $T$-cells and $B$-cells,once the infection has been cleared.
This mechanism is crucial to prevent the immune system from attacking the body's own healthy tissues,thereby maintaining immune tolerance and preventing autoimmune diseases.

(B) Agglutination is the process where antibodies bind to antigens (such as bacteria or red blood cells) to form a large,insoluble,visible clump or complex.
This reaction is commonly used in diagnostic tests to detect the presence of specific antigens or antibodies in a sample.
Therefore,the correct term for this phenomenon is Agglutination.

(B) The immune system is designed to distinguish between 'self' and 'non-self' cells.
When the immune system loses this ability and starts attacking the body's own healthy cells and tissues,this condition is known as $Autoimmunity$.
Examples of autoimmune diseases include rheumatoid arthritis and multiple sclerosis.

(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.
Injecting the microbes deliberately during immunization or infectious organisms gaining access into the body during natural infection induces active immunity.
Therefore,immunity obtained after recovering from a disease is a form of natural active immunity.

(A) Organ transplantation rejection is primarily a type of cell-mediated immune response.
$T$-lymphocytes (or $T$-cells) are responsible for cell-mediated immunity.
When a foreign organ is transplanted,the recipient's $T$-cells recognize the foreign antigens on the donor tissue and initiate an immune response to destroy the transplanted organ,leading to rejection.

(B) Passive immunity is a type of immunity where pre-formed antibodies are directly introduced into the body to provide immediate protection.
When a person is exposed to antigens like those causing tetanus or snake venom,direct injection of antibodies (antitoxins) is required to neutralize the pathogens or toxins immediately.
Unlike active immunity,which involves the body's own immune system producing antibodies in response to antigens (like vaccines),passive immunity does not involve the host's immune system in the production of antibodies.
Therefore,injecting antibodies is the correct method to obtain passive immunity.

(C) Edward Jenner of Britain in $1796$ demonstrated that vaccination with cowpox virus provides immunity and protects individuals from smallpox. This was the first successful vaccination in history.

(C) Vaccination involves the introduction of a weakened or inactivated pathogen (or its antigens) into the body.
This process stimulates the immune system to recognize the foreign antigen.
In response,the immune system produces specific proteins known as antibodies to neutralize or destroy the pathogen.
These antibodies provide immunity against future infections by the same pathogen.

(A) Humoral immunity is mediated by antibodies present in the blood and other body fluids.
These antibodies are produced by $B$-lymphocytes ($B$-cells) in response to antigens.
$T$-lymphocytes are responsible for cell-mediated immunity,not humoral immunity.
Therefore,the correct answer is $B$-lymphocytes.

(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.
Since infection by germs naturally exposes the body to antigens,the resulting immune response is classified as active immunity.

(A) An antibody,also known as an immunoglobulin $(Ig)$,is a large,$Y$-shaped protein produced by plasma cells (differentiated $B$-lymphocytes).
Its primary function is to identify and neutralize foreign objects such as bacteria and viruses.
Antibodies specifically bind to unique molecules on the surface of pathogens,known as antigens,thereby inactivating them or marking them for destruction by other immune cells.

(C) An antigen is a foreign substance,such as a toxin,bacterium,or virus,that enters the body and triggers an immune response.
Specifically,it acts as a stimulus for the immune system to produce specific proteins called antibodies to neutralize or destroy the foreign invader.
Therefore,an antigen is the stimulus for antibody formation.

(C) 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 $Active$ $immunity$.
This immunity is slow and takes time to give its full effective response.
Since the person has already suffered from the disease,their immune system has encountered the pathogen,produced specific antibodies,and formed memory cells.
Therefore,if the same pathogen attacks again,the body mounts a rapid and vigorous response,preventing the disease from recurring.

(D) Passive immunity is a type of immunity where pre-formed antibodies are directly introduced into the body to provide immediate protection.
It was discovered by Emil Von Behring and Kitasato Shibasaburo in $1890$.
They demonstrated that serum from animals immunized against diphtheria could protect other animals from the disease,a concept that led to the development of antitoxin therapy.