Immunity Questions in English

(A) The correct statement is that Helper $T$-cells stimulate the proliferation of other $T$-cells and $B$-cells in the immune response.
$A$ is correct because Helper $T$-cells ($CD4^+$ cells) release cytokines that activate and stimulate the proliferation of cytotoxic $T$-cells and $B$-cells.
$B$ is incorrect because opsonisation refers to the process of coating pathogens with antibodies to make them more susceptible to phagocytosis,not clumping (which is agglutination).
$C$ is incorrect because Helper $T$-cells are activated,not deactivated,by antigen-presenting cells.
$D$ is incorrect because Natural Killer $(NK)$ cells are part of the innate immune system,which provides non-specific defense,not specific defense.

(B) An antibody molecule consists of four polypeptide chains: two identical heavy $(H)$ chains and two identical light $(L)$ chains.
These chains are held together by disulphide $(S-S)$ bonds.
Specifically,the two heavy chains are linked to each other by disulphide bonds $(i)$.
Additionally,each light chain is linked to a heavy chain by a disulphide bond between their constant regions $(iii)$.
Therefore,the correct statements are $i$ and $iii$.

(A) Antibodies (immunoglobulins) perform several functions in the immune system,such as neutralization of toxins,agglutination of pathogens,and opsonization (coating of bacteria to facilitate phagocytosis).
However,antibodies themselves do not perform phagocytosis.
Phagocytosis is the process by which specialized cells,such as macrophages and neutrophils,engulf and digest pathogens.
Therefore,phagocytosis is a function of phagocytic cells,not of the antibodies themselves.

(C) Statement $I$ is correct because passive immunity involves the direct transfer of pre-formed antibodies to the host,providing immediate protection.
Statement $II$ is incorrect because the $BCG$ vaccine contains weakened or attenuated pathogens. When introduced into the body,it stimulates the immune system to produce its own antibodies and memory cells,which is a characteristic of Active Immunity (specifically,Artificially Acquired Active Immunity). Therefore,$BCG$ vaccination is not an example of passive immunity.

(A) Statement-$I$ is correct because $T$-lymphocytes differentiate into helper,cytotoxic (killer),memory,and suppressor $T$-cells.
Statement-$II$ is incorrect because $B$-lymphocytes mature in the bone marrow and are responsible for humoral (antibody-mediated) immunity,whereas $T$-lymphocytes are responsible for cell-mediated immunity.

(D) Vaccines are preparations of antigenic proteins of pathogen or inactivated/weakened pathogens (vaccine) which are introduced into the body to develop immunity.
They stimulate the immune system to produce antibodies and memory $B$ and $T$ cells,which recognize and eliminate the pathogen upon subsequent exposure.
Option $D$ is incorrect because the introduction of pre-formed antibodies into the body is known as passive immunization (e.g.,anti-tetanus serum),not vaccination. Vaccination involves active immunization.

(D) $1$. Immunity is classified based on how the body acquires it.
$2$. Passive immunity occurs when ready-made antibodies are transferred to an individual.
$3$. When this transfer happens through natural processes,such as the transfer of $IgA$ antibodies from mother to infant via colostrum,it is termed 'natural acquired passive immunity'.
$4$. Since the infant does not produce these antibodies themselves,it is passive,and because it occurs through a natural biological process (breastfeeding),it is natural.

(A) Sensitized helper $T$-cells (also known as $CD4^+$ $T$-cells) play a crucial role in the immune response by coordinating other immune cells.
Upon activation by antigens presented by antigen-presenting cells,these cells secrete signaling proteins known as lymphokines.
Lymphokines act as chemical messengers that stimulate the proliferation and activation of $B$-cells,cytotoxic $T$-cells,and macrophages,thereby enhancing the overall immune response.
Lysozyme is an enzyme found in secretions like tears and saliva,perforins are produced by cytotoxic $T$-cells and natural killer cells to destroy target cells,and lysin is a general term for substances that cause lysis.

(A) When a person is exposed to an antigen (like the measles virus) through a natural infection,the body's immune system produces antibodies and memory cells in response to the pathogen.
This type of immunity is known as $Natural \ Acquired \ Active \ Immunity$.
It is 'natural' because it occurs through natural exposure to the disease,'acquired' because it is developed during an individual's lifetime,and 'active' because the host's own immune system actively produces the antibodies.

(B) Antibodies are specialized proteins called immunoglobulins that are produced by $B$-lymphocytes (a type of white blood cell) in response to antigens.
When $B$-lymphocytes are activated,they differentiate into plasma cells,which are the primary cells responsible for the synthesis and secretion of antibodies into the blood and lymph.
Therefore,the correct answer is $B$-lymphocyte.

(B) Cytotoxic $T$-cells are also known as $CD8^+$ $T$-cells or Killer $T$-cells.
They are a specialized type of $T$-lymphocyte that directly kills infected host cells (such as those infected by viruses) or cancerous cells.
They recognize antigens presented on the surface of cells by $MHC$ class $I$ molecules and induce apoptosis in the target cells.
Therefore,the correct option is $B$.

(A) The introduction of attenuated (weakened) pathogens into the human body is the principle behind vaccination.
When these weakened pathogens are introduced,the immune system recognizes them as foreign antigens and triggers an immune response.
This leads to the production of antibodies and memory cells by the host's own immune system.
Since the body actively produces its own antibodies in response to an external,non-natural stimulus (vaccine),this type of immunity is known as $Artificial$ $acquired$ $active$ $immunity$.

(C) Helper $T$-cells secrete chemical messengers known as lymphokines,which stimulate other immune cells.
Similarly,Killer $T$-cells (also known as Cytotoxic $T$-cells) release proteins called perforins.
Perforins create pores in the membrane of infected or target cells,leading to their lysis and destruction.
Therefore,the correct analogy is Killer $T$-cells : Perforins.

(C) Plasma cells are specialized effector cells of the immune system that secrete large quantities of antibodies.
They are differentiated from activated $B$-lymphocytes ($B$-cells) upon exposure to an antigen.
When a $B$-cell encounters its specific antigen and receives signals from helper $T$-cells,it undergoes clonal expansion and differentiates into plasma cells and memory $B$-cells.
Therefore,plasma cells are derived from $B$-lymphocytes.

(C) The thymus gland is a primary lymphoid organ that plays a crucial role in the development and maturation of $T$-lymphocytes,which are essential for cell-mediated immunity.
As a person ages,the thymus gland undergoes a process called involution,where it gradually shrinks and is replaced by adipose tissue.
This degeneration of the thymus gland leads to a reduced production and maturation of $T$-cells,which significantly weakens the immune system in elderly individuals.

(B) Secondary lymphoid organs are the sites where lymphocytes interact with the antigen and then proliferate to become effector cells. These include the spleen,lymph nodes,tonsils,Peyer's patches of the small intestine,and the appendix. Bone marrow and the thymus are primary lymphoid organs where immature lymphocytes differentiate into antigen-sensitive lymphocytes. Therefore,the group consisting of the appendix,tonsils,and Peyer's patches of the small intestine represents secondary lymphoid organs.

(A) Colostrum is the yellowish fluid secreted by the mother during the initial days of lactation.
It contains abundant antibodies,specifically $IgA$,which are essential to develop resistance in the newborn baby.
Since the antibodies are provided directly to the infant rather than being produced by the infant's own immune system,this is an example of passive immunity.
Therefore,the correct option is $A$.

(C) $IgE$ antibodies are primarily involved in allergic reactions.
When an allergen enters the body,it binds to $IgE$ antibodies attached to the surface of mast cells and basophils.
This binding triggers the degranulation of these cells,leading to the release of inflammatory mediators like histamine and serotonin,which cause the symptoms of an allergy.
Therefore,$IgE$ is responsible for providing an immune response to allergens.

(D) When ready-made antibodies are directly introduced into the body to provide immediate protection against foreign antigens or pathogens,this type of immunity is known as $Passive \ immunity$. Examples include the transfer of $IgA$ antibodies from mother to infant through colostrum or the administration of anti-tetanus serum.

(B) The correct matching is as follows:
$1$. Cellular barrier: These include cells like polymorphonuclear leukocytes ($PMNL$-neutrophils),monocytes,and natural killer (type of lymphocytes) in the blood. Thus,$1-C$.
$2$. Physiological barrier: These include acid in the stomach,saliva in the mouth,and tears from eyes,which prevent microbial growth. Thus,$2-A$.
$3$. Cytokine barrier: Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection. Thus,$3-B$.
$4$. Physical barrier: These include the skin and the mucus coating of the epithelium lining the respiratory,gastrointestinal,and urogenital tracts. Thus,$4-D$.
Therefore,the correct sequence is $(1-C), (2-A), (3-B), (4-D)$,which corresponds to option $B$.

(C) When ready-made or preformed antibodies are directly injected into the body to provide a quick immune response,it is known as passive immunity.
In the case of snakebites,the patient needs immediate protection because the venom acts rapidly.
Since the body does not have enough time to produce its own antibodies (which would be active immunity),preformed antibodies are administered to neutralize the toxin immediately.
Therefore,the correct answer is $C$ (Passive immunity).

(B) Interferons are proteins secreted by virus-infected cells which protect non-infected cells from further viral infection.
These proteins act as a cytokine barrier in the innate immune system.
Therefore,the secretion of interferon is a cytokine barrier.

(D) In the human body, primary lymphoid organs are the sites where lymphocytes originate and/or mature and become antigen-sensitive.
These organs include the $Bone marrow$ and the $Thymus gland$.
In the $Bone marrow$, all blood cells including lymphocytes are produced.
In the $Thymus gland$, $T$-lymphocytes mature.
Therefore, both $Bone marrow$ and $Thymus gland$ are primary lymphoid organs.

(A) Innate immunity consists of four types of barriers: physical,physiological,cellular,and cytokine barriers.
$1$. Physical barriers include skin and mucus coatings.
$2$. Physiological barriers include acid in the stomach,saliva in the mouth,and tears from eyes.
$3$. Cellular barriers include leukocytes like polymorphonuclear leukocytes ($PMNL$-neutrophils),monocytes,and natural killer cells.
$4$. Cytokine barriers involve virus-infected cells that secrete proteins called interferons,which protect non-infected cells from further viral infection.
Therefore,the correct answer is $A$.

(A) An auto-immune disease occurs when the immune system mistakenly attacks the body's own healthy cells and tissues.
Rheumatoid Arthritis is a classic example of an auto-immune disease where the immune system attacks the joints,causing inflammation and pain.
Malaria is an infectious disease caused by protozoa.
Cancer is a disease characterized by uncontrolled cell division.
$AIDS$ is an immunodeficiency disease caused by the $HIV$ virus.

(A) Passive immunity (or passive resistance) occurs when ready-made antibodies are directly given to the body to protect against a foreign agent.
$A$. Polio vaccine (oral) contains weakened pathogens that stimulate the body to produce its own antibodies,which is an example of active immunity.
$B$. Vaccine against snake venom (antivenom) contains pre-formed antibodies,which is passive immunity.
$C$. Colostrum contains $IgA$ antibodies transferred from mother to infant,which is natural passive immunity.
$D$. Tetanus antitoxin contains pre-formed antibodies,which is passive immunity.
Therefore,the Polio vaccine is the only option that relates to active immunity rather than passive resistance.

(A) The correct answer is $IgA$.
Colostrum is the yellowish fluid secreted by the mother during the initial days of lactation.
It contains abundant antibodies,specifically $IgA$,which are essential to provide passive immunity to the newborn infant.

(D) Interferons are antiviral proteins secreted by virus-infected cells to protect neighboring healthy cells. They are part of the innate immune system. None of the provided options $(A, B, C, D)$ are known to specifically inhibit the secretion of interferons in a physiological context. Viral infection actually stimulates the production of interferons. Therefore,the question is scientifically flawed as none of the options act as an inhibitor of interferon secretion.

(A) The principle of vaccination is based on the property of 'Memory' of the immune system.
During vaccination,an inactivated or weakened pathogen (vaccine) is introduced into the body.
The immune system recognizes the antigen and produces specific antibodies against it.
Crucially,the immune system also generates memory $B$ and $T$ cells.
When the body encounters the actual pathogenic agent later,these memory cells recognize the pathogen immediately and produce a massive amount of antibodies to neutralize the infection.
Therefore,the correct option is $A$.

(D) passive immunisation.
When a person is exposed to deadly microbes (like those causing tetanus or snake bites),there is no time to wait for the body to produce its own antibodies. In such cases,preformed antibodies or antitoxins are directly injected into the patient's body to provide an immediate immune response. This type of immunity is known as passive immunisation.

(D) The correct answer is $D$.
Passive immunity is a type of immunity that occurs when ready-made antibodies are introduced directly into the body to provide immediate protection against foreign pathogens or toxins.
In the case of a snake bite,the patient is injected with an antivenom,which contains preformed antibodies specifically designed to neutralize the snake venom.
Since the body's own immune system is not actively involved in producing these antibodies,this process is classified as passive immunization.

(B) The incorrect statement is: $B$. Interferons kill viruses.
Interferons are glycoproteins produced by virus-infected cells. They do not kill viruses directly; instead,they protect non-infected cells from further viral infection by inhibiting viral replication.

(C) Natural killer $(NK)$ cells are a type of white blood cell that plays a major role in the host-rejection of both tumors and virally infected cells.
In the context of innate immunity,the human body has four types of barriers:
$1$. Physical barriers: e.g.,skin,mucus coating of the epithelium.
$2$. Physiological barriers: e.g.,acid in the stomach,saliva in the mouth,tears from eyes.
$3$. Cellular barriers: e.g.,polymorphonuclear leukocytes ($PMNL$-neutrophils),monocytes,macrophages,and natural killer lymphocytes.
$4$. Cytokine barriers: e.g.,interferons.
Therefore,natural killer lymphocytes are classified under cellular barriers.

(B) $Interferons$ are protein molecules produced by virus-infected host cells.
They help in the defense against viral infections by signaling neighboring cells to enhance their antiviral defenses.
While normal cells can produce other proteins,$Interferons$ specifically come from infected cells.

(D) The correct matching is as follows:
$A$. Natural active immunity: This occurs when the body encounters a pathogen and develops an immune response naturally,i.e.,$s$. Fighting infections naturally.
$B$. Artificial passive immunity: This involves the administration of pre-formed antibodies (antiserum) to provide immediate protection,i.e.,$r$. Injection of antiserum to travellers.
$C$. Artificial active immunity: This is induced by introducing antigens into the body through vaccination to stimulate an immune response,i.e.,$t$. Induced by vaccination.
$D$. Natural passive immunity: This occurs when antibodies are transferred from mother to foetus through the placenta or via colostrum,i.e.,$q$. From mother to foetus through placenta.
Therefore,the correct combination is $A-s, B-r, C-t, D-q$.

(B) Active immunity involves the body producing its own antibodies in response to an antigen.
Passive immunity involves the direct injection of pre-formed antibodies,as seen in the case of antitoxins for snake venom,tetanus,or diphtheria.
This provides immediate protection,which is the characteristic feature of passive immunization.