Acquired immunity - class-IX

Passive immunity involves the transfer of pre-formed antibodies to an individual. IgA is a key antibody found in breast milk, which provides passive immunity to infants.

Naturally acquired passive immunity is a type of antibody-mediated immunity conveyed to a fetus or infant by its mother. In humans, maternal antibodies are passed through the placenta to the fetus by an FcRn receptor on placental cells.

In humoral response the antibodies are produced by the B cells

Antibodies are immune system-related proteins called immunoglobulins. Each antibody consists of four polypeptides– two heavy chains and two light chains joined to form a "Y" shaped molecule. Antibodies are produced by specialized white blood cells called B lymphocytes (or B cells). When an antigen binds to the B-cell surface, it stimulates the B cell to divide and mature into a group of identical cells called a clone.

A lymphocyte is one of the subtypes of white blood cell in a vertebrate's immune system. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic adaptive immunity), and B cells (for humoral, antibody-driven adaptive immunity). They are the main type of cell found in lymph. Lymphocytes are involved in the activation of the immune system.

Humoral immunity is the aspect of immunity that is mediated by macromolecules found in extracellular fluids such as secreted antibodies, complement proteins, and certain antimicrobial peptides. Humoral immunity is so named because it involves substances found in the humour (plasma or lymph) or body fluids. It involves antibody, so, it is often referred to as antibody-mediated immunity.

A T cell, or T lymphocyte, is a type of lymphocyte (a subtype of white blood cell) that plays a central role in cell-mediated immunity. T cells can be distinguished from other lymphocytes such as B cells and natural killer cells by the presence of a T-cell receptor on the cell surface. T-cells are produced from the bone marrow. They are called T cells because they mature in the thymus from thymocytes.

Humoral immunity is the type of acquired immunity and it includes the action of antibodies. When system observe any antigen or foreign agent inside the body id activates the B-cell and fit converted into immunocompetent B-cells. Further, they get activated and form functional B cells, which are present on plasma cells and release the antibody formed.

It is a type of immunity that does not involve antibody but includes phagocytosis which provides protection against pathogens. Presence of pathogens activate T-lymphocytes and convert it into effector T-cells and bind to APCs and release the enzyme like perforins which helps in the destruction of the cell which is infected.

Plasma cells of B-lymphocytes are derived from the memory B-lymphocytes and are involved in the production of antibodies actively in the blood.

The B-lymphocytes are the types of immune cells that are involved in the humoral immune response. It means these cells are responsible for making antibodies in the bloodstream and destroy the antigen that infects the blood and tissues via blood. T-cells are responsible for cell-mediated immunity. They wipe out those pathogens that invade the tissues directly. B-cells can exist in two forms- Memory B-cells that are specified for a particular infection and Plasma B-cells that actively secrete antibodies. Plasma B-cells are derived from the memory B-cells whenever that specific antigen invades the blood second time.

The body's immune system is a normally occurring protective mechanism that helps the body defend itself against harmful agents. However, sometimes the immune system perceives normally harmless substances such as allergens or the person's own body tissues as harmful invaders and try to eliminate them. This inappropriate activation of the immune response is a major factor in allergic and auto-immune disorders.
Immunosuppressants are the drugs that suppress the immune to reduce the risk of rejection of foreign bodies with organ transplants or in auto-immune disorders.
B-cells are lymphocytes capable of producing antibodies and can capture circulating antigens. They are produced from stem cells in the bone marrow of adult mammals, liver of foetus and bursa of Fabricius in birds. The mature B-cells synthesize various types of antibodies which are displayed on their membrane surfaces, hence they are called immuno-competent B-cells. They are the cause of Humoral immunity.
T-cells are the lymphocytes that can recognize antigens if presented by antigen-presenting cells (APCs) by MHC molecules. They are the cause of cell-mediated immunity. Therefore, both B-cells and T-cells reveal the immunosuppressants on their surface and are part of the immune system.
Alpha cells are one of the types of cells in the Islets of Langerhans in the endocrine portion of the pancreas, which produces the hormone glucagon that is secreted in response to hypoglycemia.

• So the correct option is 'Both 1 & 3'.

B-lymphocytes form army of proteins called antibodies in response to pathogen in blood and are stimulated by antigen and T-helper cells. Therefore, B-lymphocytes provide humoral mediated immunity. T- lymphocytes provide cell mediated immunity. So, the correct option is 'B-lymphocytes'.

Acquired immunity is developed after birth. It is produced after getting exposed to antigens hence it is specific in nature. Acquired immunity creates immunological memory after an initial response to a specific pathogen, and leads to an enhanced response to subsequent encounters with that pathogen.

The T-lymphocytes originate in hematopoietic stem cells in the bone marrow and mature in the thymus. T-lymphocytes are responsible for humoral immunity. There are different types of T cells. They are listed below:

Cell mediated immunity is  macrophage providing an antigen for the T cells, so that the infected cells can be targeted

Adaptive immunity is often sub-divided into two major types depending on how the immunity was introduced. 'Naturally acquired immunity' occurs through contact with a disease causing agent, when the contact was not deliberate, whereas 'artificially acquired immunity' develops only through deliberate actions such as vaccination.

Acquired immunity or adaptive immunity develops following exposure to an antigen and is mediated by B lymphocytes or T lymphocytes or both, having a specific surface receptor for the same antigen.
Following are the characteristics of acquired immunity:

• Diversity: They can respond to millions of different antigens.
• Antibody specificity: Ability of the antibody to recognize the specific antigen (even antigen molecule differing by a single amino acid). The response is directed only towards the initiated pathogen.
• Immunologic memory: Once recognized and responded to an antigen, the system is able to respond more strongly to subsequent exposure even after many years.
• Discrimination between self and non-self: It can differentiate self-cells (host cells) from foreign cells and molecules. Only foreign particles are attacked. Failure of this discrimination results in auto-immune diseases.

During infection, B-cell receptor binds to the antigens and these bound antigens are engulfed into the B-cells by receptor-mediated endocytosis. The antigens are then degraded, and presented to T cells in complex with MHC-II (major histocompatibility complex - II) molecules on the cell membrane. T-cells bind to the B-cells and secretes lymphokines due to which B-cell undergo proliferation and produce antibodies specific to the antigen.

An antigen is a foreign substance which produces an immune response and is specifically bound to antibodies. Each antibody is specifically produced by the immune system to match an antigen after cells in the immune system come into contact with it, this allows a precise identification or matching of the antigen. Antigens are usually proteins, peptides and polysaccharides which elicit an immune response.

A cytotoxic T-cell, also known as Killer T-cells is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected (particularly with viruses), or cells that are damaged in other ways. When killer T-cells are exposed to antigens, they release the cytotoxins perforin, granzymes, and granulysin. Perforins and granzymes causes pore formation in the antigen which causes the intracellular content of antigen to leak out resulting in cell death.

Memory cells are formed from T-lymphocytes because memory T cells have the ability to recognized specific antigen. They will activate a stronger and faster immune response after they come across the same antigen again

The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, T cells mature. T cells are critical to the adaptive immune system, where the body adapts specifically to foreign invaders. The thymus is the largest and most active during the neonatal and pre-adolescent periods.  Surgical removal of the thymus results in immunodeficiency because T- cells do not undergo maturation and this results in suppression of the immune system. 

They have a long life which might start from few months and range to their entire life.

Humoral immunity is a type of immunity which is mediated by macromolecules found in extracellular fluids such as secreted antibodies, complement proteins, and certain antimicrobial peptides. Humoral immunity is so named because it involves substances found in the humour or body fluids. It involves B-lymphocytes or plasma cells and is often known as antibody-mediated immunity.

• T-cells are a type of white blood cell that plays a central role in cell-mediated immunity. 
• T-helper cell assists other white blood cells in immunologic processes, including maturation of B cells into plasma cells and memory B cells and activation of cytotoxic T cells and macrophages. These cells are also known as CD4+ T cells because they express the CD4 glycoprotein on their surfaces.
• Cytotoxic T-cells destroy virus-infected cells and tumour cells and are also implicated in transplant rejection. These cells are also known as CD8+ T cells since they express the CD8 glycoprotein at their surfaces.
• So, the correct answer is 'CD 4'.

• The immune system is a host defence system comprising many biological structures and processes within an organism that protects against disease.  The immune system can be classified into subsystems such as the innate immune system and the adaptive immune system, or humoral immunity and cell-mediated immunity. 
  
• Humoral immunity is the aspect of immunity that is mediated by macromolecules found in extracellular fluids such as secreted antibodies, complement proteins, and certain antimicrobial peptides.
  
• Cell-mediated immunity is an immune response that does not involve antibodies, but rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.
  

T cell is a type of WBC that plays a central role in cell-mediated immunity. They are called T cells because they mature in the thymus from thymocytes. T cells kill the pathogen by producing - 

• A cytotoxic T cell (also known as TC, cytotoxic T lymphocyte, CTL, T-killer cell, cytolytic T cell, CD8+ T-cell or killer T cell) is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected (particularly with viruses), or cells that are damaged in other ways..
  
• They have CD - 8 markers on the cell membrane.
•  When cytotoxic T cells recognize (bind to) their target, they produce more FasL at their surface. This binds with the Fas on the surface of the target cell leading to its death by apoptosis. Hence The cells which have CD - 8 markers on the cell membrane are T-cytotoxic cells.
• So, the correct answer is 'T-cytotoxic cells'.

The humoral immune response is governed by the antibodies that are secreted by the activated B cells. These are activated by Immunoglobulins A(IgA).

So, the correct option is ‘IgA’.

• A mast cell is a resident cell of connective tissue that contains many granules rich in histamine and heparin.
• Mast cells are allergy cells responsible for immediate allergic reactions. They cause allergic symptoms by releasing Histamine and heparin.
  
• Hence the chemicals secreted by damaged mast cell of connective tissue are Histamine and heparin.
• So, the correct answer is 'Histamine and heparin'.

A- B cells differentiate into plasma cells that produce antibody molecules closely modeled after the receptors of the precursor B cell. Once released into the blood and lymph, these antibody molecules bind to the target antigen (foreign substance) and initiate its neutralization or destruction.

The specific region on an antigen that an antibody recognizes and binds to is called the epitope, or antigenic determinant. An epitope is usually 5-8 amino acids long on the surface of the protein. Proteins are three dimensionally folded structures, and an epitope may only be recognized in its form as it exists in solution, or its native form. The antigen binding portion of an antibody varies extensively among secreted antibodies, and this length of sequence is known as the variable region. The variable region construction during antibody production in the B cell is what enables antibodies to be generated against an infinite variety of antigens. The other biological properties of the antibody and its role in signaling to other immune cells are determined by the constant regions of the heavy chains.

A- IL-1α is produced mainly by activated macrophages, as well as neutrophils, epithelial cells, and endothelial cells. It possesses metabolic, physiological, haematopoietic activities, and plays one of the central roles in the regulation of the immune responses. It binds to the interleukin-1 receptor.

a) HLA system is also called as human leukocyte antigen system. It is a gene complex which encodes for the major histocompatibility complex (MHC) in humans. HLA haplotype is the set of histocompatibility genes that are on the same chromosome and are inherited together. Each individual inherits one pair of HLA haplotypes from each parent. 

Thymosins are proteins present in animal tissues. They have diverse biological activities. It is serrated by the thymus gland and it is important because it stimulates the development of T.lymphocytes also known as killer T.blood cells. It also functions in the immune system to recognize foreign antigens on the surface of cells.

B cells, otherwise called B lymphocytes, are a sort of white platelet of the lymphocyte subtype. They work in the humoral insusceptibility segment of the versatile safe framework by emitting antibodies. 

Immunocompetence is the ability of the body to produce a normal immune response following exposure to an antigen. Immunocompetence is the opposite of immunodeficiency.

The immune system has two divisions-humoral immunity and cell-mediated immunity. The humoral immunity protects against extracellular pathogens while the cell-mediated immunity protects against intracellular pathogens.

Activated B cells differentiate into either antibody-producing cells called plasma cells that secrete soluble antibody or memory cells that survive in the body for years afterwards in order to allow the immune system to remember an antigen and respond faster upon future exposures.

The activity of complement components is modulated by a system of regulatory proteins that prevent tissues damage as a result of inadvertent binding of activated complement components to host cells or spontaneous activation of complement components in plasma.