Adaptive immunity,acquired immunity

Chapter 17

Adaptive Immunity and immunization

Adaptive immunity ,acquired immunity, obtained in some manner other than heredity. provides specific, nonhereditary defense and protection after exposure to a specific pathogen.

(A).Naturally acquired adaptive immunity is Adaptive immunity,acquired immunity obtained by having a specific disease. The immune system respond to antigens, activates T cells, produces antibodies to protect against the same disease. Colostrum is the first fluid secreted by the mammary Adaptive immunity,acquired immunity glands after childbirth. It contains a lot of antibodies. Only protect for a short time then disappear.

Naturally acquire passive immunity refers to the antibodies across the placenta and in breast milk.

(B Adaptive immunity,acquired immunity).Artificially acquired adaptive immunity is obtained by the injections of vaccine that produces immunity.

All animals have an innate immune system. Only vertebrates have an adaptive immune system.

^ Active and Passive Adaptive immunity,acquired immunity Immunity

In active immunity, an individual’s own immune system makes antibodies.

In passive immunity, ready-made antibodies are introduced into the body.

Naturally acquired passive immunity is by receiving antibodies from Adaptive immunity,acquired immunity planceta or in colostrums

Artificially acquired passive immunity is by receiving injection of gamma globulin or immune serum



An antigen is a foreign substance that can elicit a specific immune Adaptive immunity,acquired immunity response. Most antigens are proteins, but some are polysaccharides, nucleoproteins, or glycoproteins.

Each antigen has several epitopes (antigenic determinants), or antigenic determinants.

Hapten: a small molecules can acts as an antigen only Adaptive immunity,acquired immunity if it binds to a larger protein molecule.

Generating antibody diversity

The diversity of B cell receptors is sufficient to recognize epitopes on any pathogen we are likely to encounter in our Adaptive immunity,acquired immunity life time.

B-cell diversity is generated by recombining epitopes on any pathogen we are likely to encounter in our life time.

B-cell diversity is generated by recombining bits of DNA in our genome Adaptive immunity,acquired immunity to generate 100 millions different antibody genes.

^ Cells and Tissues of the Immune System

Lymphocytes develop from lymphoid stem cells in the bone marrow. Lymphocytes differenciate into B cells in the Adaptive immunity,acquired immunity bone marrow or into T cells in the thymus.

Subsequent differentiatoion of T cells produces four different kinds of cells

1). Cytotoxic (killer) T cells

2). Delay-hypersensitivity T cells

3). Helper T cells

4). Regulatory T cells.

Natural killer cells (NK cells Adaptive immunity,acquired immunity), non B, non T cells, which nonspecifically kill cancer cells and cells infected with virus without having to utilize the specific immune responses. By releasing cytotoxic molecules to create Adaptive immunity,acquired immunity holes in the target’s cell membrane , leading to lysis.Other molecules enter the target cell and fragment DNA, causing apoptosis(programmed cell death). NK cells are also affected by interferons.

^ Dual nature of the Adaptive immunity,acquired immunity Immune Syetem

The dual roles of the immune system consist of humoral immunity, which is carried out mainly by antibodies produced by B cells and plasma cells, and cell mediated immunity, which is Adaptive immunity,acquired immunity carried out mainly by certain T cells.

General Properties of Immune Responses

When our first line of defense is breached and our innate immune system fails to control an infection, our adaptive immune Adaptive immunity,acquired immunity system is activated.


Major Histocompatibility Complex

^ MHC Class 1: receptors on all cells, identify as self, present antigen for systemic. Recognized by CD8 Cytotoxic T cells.

MHC Class 2: leukocytes only, intercelluar communication Adaptive immunity,acquired immunity. Recognized by CD4 Helper T cells.

MHC Class 3: all protein produces as listed above

^ Self: Class1 receptors on Neutrophils/Macrophage must match

Nonself: Class 2 receptors do not match phagocytosis

1). Recognition of self versus nonself

Embryos Adaptive immunity,acquired immunity contain many different lymphocytes, each genetically programmed to recognize a particular antigen and make antibodies to destroy it. A lymphocyte divides repeatedly to produce a clone.

According to the clonal selection theory, B cells recognize Adaptive immunity,acquired immunity specific epitopes on antigens according to the particular antibody present on the B cell plasma membrane. When a B cell detects an antigen with which it can react, it binds to the Adaptive immunity,acquired immunity antigen, engulfs it, process it, displays a peptide fragment as MHC class II to TH2 cells, and divides many times.

^ Clone of genetically identical B cells, which differentiate into Adaptive immunity,acquired immunity many plasma cells and some memory cells, is produced.

Tolerance is B or T cells encounters its programmed antigen as part of a normal host substance (self).

2). Specificity

Immune system fully matures at age Adaptive immunity,acquired immunity 2 to 3.

Specificityrefers to the ability of immune responses to respond to and distinguish among different antigens and epitopes.

Cross-reaction , reactions of a particular antibody with very similar antigens.

^ 3). Heterogeneity (Diversity)

Diversity refers Adaptive immunity,acquired immunity to the ability of immune responses to produce many different antibodies and cell substances on the basis of the different antigens they encounter.

4). Memory

Ability of T and B cells Adaptive immunity,acquired immunity can recognize substances it has previously encountered- memory cells.

Anamnestic (secondary) response is prompt due to recall of memory cells.

The power and rapid secondary immune response initiated by memory B cellsacts within Adaptive immunity,acquired immunity few days, sometimes suppressing all symptoms.

The action of vaccines depends upon their stimulating the formation of memory B cells.


Cell Mediated – involves different cells and their secretory products

Antibody mediated – production, secretion Adaptive immunity,acquired immunity and action of antibodies


Antibody Mediated Response: plasma B cells synthesize and secrete antibody

Functions: to bind antigen agglutination

Fix complements chemotaxis leukokine production

Inhibits microbe attachment inhibits microbe motility decrease infectious


“goal” to Adaptive immunity,acquired immunity neutralize antigen, prevent reproduction of microbe, prevent further invasion, to decrease the number of infectious particles.

^ B-cell activation

Native B cells are fully differentiated B cells that have not yet encountered Adaptive immunity,acquired immunity a complementary antigen; they bear membrane–bound IgM and IgD on their outer surface.

Clonal selection begins when native B cells bind to their complementary antibodies: Then they multiply; produce soluble IgM Adaptive immunity,acquired immunity and IgD, and undergo a high rate of mutation in their DNA-encoding region, resulting in affinity maturation.

Later, class switching occurs: Various activated B cells begin to make all classes of Adaptive immunity,acquired immunity antibodies.

Some members of the clone become short-lived effectors (plasma) cells, which make large quantities of antibody; others become long-lived memory cells, which fight future infections by the same pathogen.

Lymphocytes, including Adaptive immunity,acquired immunity interleukins-1,-2,-4,-5, and -6, produced by NK cells help B-cell activation stimulated by most antigens. Some T-independent antigens stimulate B-cell activation without help.

B cells are selected to Adaptive immunity,acquired immunity respond to specific antigens in accordance with the particular antibody present on the B cell membrane prior to encountering an antigen.

When a B cell detects an antigen with which it can react, it Adaptive immunity,acquired immunity binds to the antigen (sensitized or activates) and divides many times to produce a clone of many plasma cells and some memory cells.

Many B cells require helper T cells Adaptive immunity,acquired immunity to proliferate and differentiate into both plasma and memory B cells.

^ Plasma cells synthesize and release large numbers of antibodies.

Memory cells remain in lymphoid tissues ready to respond to subsequent exposure Adaptive immunity,acquired immunity to the same antigen.

Properties of Antibodies (Immunoglobulins)

Antibodies are glycoproteins because carbohydrate groups are attached to them.Structually, antibodies consist of two heavy and two light polypeptide chains, joined by disulfide bonds to form Adaptive immunity,acquired immunity a Y shape.

The upper ends of the Y, consists of variable region in both the light and heavy chains, differ from antibody to antibody.

These variable regions form the two antigen Adaptive immunity,acquired immunity-binding sites (part of the Fab fragment), which are responsible for the specificity of the antibody.

The remaining part of the molecule consists of constant regions (Fc) that are Adaptive immunity,acquired immunity similar in all antibodies of a particular class. The constant region binds to and activates phagocytes and complement.

Know Antibody structure in Figure 17.7.

^ Class of Immunoglobins

Five classes of immunoglobulins have been identified Adaptive immunity,acquired immunity. Each class has a particular kind of constant region which gives that class its distinguishing properties. IgD, IgE, and IgG are secreted as monomers, IgM as pentamers, and IgA as monomers or dimmers.

^ 1). IgG

The Adaptive immunity,acquired immunity main class of antibodies found in blood, accounts 20 percent of all plasma proteins.

IgG is produced in large quantities during a secondary response.

The antigen-binding sites of IgG attach to antigens Adaptive immunity,acquired immunity on microorganisms and their tissue-binding sites attach to receptors on phagocytic cells.

IgG is the only immunoglobulin that can cross the placenta from mother to fetus and provide antibody protection Adaptive immunity,acquired immunity.

IgG – monomer, predominant type, specific immune response,

transmammary, transplacental

^ 2). IgA

Occurs in small amounts in blood and in larger amounts in body secretions such as tears, milk, saliva, mucus and linings of GI Adaptive immunity,acquired immunity tracts.

Secretory IgA, which consists of two monomer units held together by a J chain, has an attached secretory component, which protects the IgA from proteolytic enzymes and facilitates its transport Adaptive immunity,acquired immunity.

Mucosal surfaces such as in the respiratory , GI tracts are major sites for invasion by pathogens.

The main function of IgA is to bind antigens on microorganisms before they invade. It also activates complement, which Adaptive immunity,acquired immunity helps to kill the microorganisms.

IgA – monomer (plasma), dimer (mucus/saliva/tears/milk/intestinal

secretions), inhibit microbe attachment to epithelia

3). IgM

IgM is found as a monomer on the surface of B Adaptive immunity,acquired immunity cells and is secreted as a pentamer by plasma cells.

IgM consists of five units connected by their tails to a J chain and has 10 peripheral antigen-binding sites.

As ^ IgM binds Adaptive immunity,acquired immunity to antigens, it also activates complement and causes microorganisms to clump together.

High levels of IgM indicate recent infection or expose to antigen.

IgM – monomers (antigen receptor) penerates (plasma), nonspecific

immune Adaptive immunity,acquired immunity response, blood typing

4). IgE

IgE has a special affinity for receptors of basophils in blood or mast cells in tissue.

It binds to these cells by tissue binding sites, leaving antigen-binding sites free to bind antigens Adaptive immunity,acquired immunity which can develop allergy. When IgE binds antigens, the basophils and mast cells secrete histamine which produce allergy symptoms. IgE are elevated in patients with allergies and worm parasites Adaptive immunity,acquired immunity.

IgE – monomer, tonsils, skin, mucus membranes. Stimulates basophils to

release histamine

5) IgD

IgD, monomer, is found mainly on B-cell membranes and function is unknown.Only trace amount.

^ Primary and Secondary Responses

Primary responses are the immune system Adaptive immunity,acquired immunity’s first encounter with foreign antigens.

First produce IgM, then IgG. Memory cells remain in lymphoid tissue, ready to respond to subsequent exposure to the same antigen.

The primary response of Adaptive immunity,acquired immunity B cells can occur by two mechanisms.

a). ^ T-independent antigens - B cells can be activated by binding antigen, proliferating and forming plasma cells.

b). T-dependent antigens – B cells Adaptive immunity,acquired immunity becomes an antigen presenting cell, and activate the T helper cell (TH). The activated TH cells then secretes lymphokines that further activate the B cell causing it to differentiate and proliferate producing B memory cells Adaptive immunity,acquired immunity and TH memory cells.

^ Secondary responses bring fast and efficient destruction of antigens recognized by B and T memory cells.

IgM is produced in a smaller quantities and IgG is Adaptive immunity,acquired immunity produced in much larger quantities than in primary response.

Kinds of Antigen-Antibody Reactions

Humoral immunity depends upon the production of antibodies by B cells.

Antibodies protect against invading microbes by neutralization, opsonization, and activating Adaptive immunity,acquired immunity complement.

Humoral immunity is most effective against bacteria, antigen-antibody reaction result in agglutination (clumping).

1). Neutralization of pathogens and toxins by IgA or IgG.

2). Opsonization of bacteria by IgG, which is activated Adaptive immunity,acquired immunity by antigen-bound IgM or IgG, produces complement C3b ,a powerful opsonin, they coat microbes so that they can be phagocytized.

3). Cell lysed by complement after or directly Adaptive immunity,acquired immunity by IgMs or IgG immune complexes


Monoclonal antibodies are antibodies produced in the laboratory from a clone of cultured cells that make one specific antibody to one specific epitope.

Specific monoclonal antibodies Adaptive immunity,acquired immunity can be used in some diagnostic tests, and methods to use them in treating infectious diseases and cancer are being developed.


Lymphocytes are small, smooth, round leukocytes that lack granules.

There are three Adaptive immunity,acquired immunity kinds of leukocytes: B cells, T cells, and natural killer (NK) cells.

B cells and T cells are triggered into defensive action when they encounter antigens, which are foreign molecules we lack.

B Adaptive immunity,acquired immunity cells respond to antigen by producing antibodies.

^ Cytotoxic T (CD8) cells respond to antigen by killing our own pathogen-infected cells.

Helper T (CD4) cells respond by stimulating phagocytes and B cells Adaptive immunity,acquired immunity.

Lymphoid Tissues

Primary lymphoid tissues are the bone marrow where blood cells, including lymphocytes, are formed and where B cells differentiate; the thymus is where T cells differentiate.

Differentiated B and T cells travel Adaptive immunity,acquired immunity to secondary lymphoid tissues, where they are stored and interact.

^ Secondary lymphoid tissues include lymph nodes, spleen, tonsils, adenoids, appendix, and Peyer’s patches.

Spleen is the largest lymph organ Adaptive immunity,acquired immunity.

Lymph is formed in our tissues as fluid from blood leaks across capillary walls.

A system of lymph vessels collects lymph and returns it to th thoracic duct that empties into the heart Adaptive immunity,acquired immunity.

Lymphocytes circulate through blood and lymph.

Lymphatic vessels and lymph nodes usually become swollen and inflamed during infections that activate an immune response.

^ The Cell-Mediated Immune Reaction

Cell mediated Response Adaptive immunity,acquired immunity:

Cytotoxic (CD8) T cells, with the aid of helper (CD4 or Th cells) T cells, are responsible for cell-mediated immunity.

Activated T helper cells in turn activate other cells and processes clonal Adaptive immunity,acquired immunity expansion of undifferentiated B cells.

B cell differentiation creates memory B and Plasma B

Plasma B synthesize and secrete antibodies which neutralize antigen

Memory T cells

Nature Killer cells

Cytotoxic T cells

Leukokine production of all leukocytes

Involves ^ T cells Adaptive immunity,acquired immunity, requires presentation of the antigen on the surface of cell with major histocompatibility complex (MHC) proteins by antigen presenting cells.

Antigen Recognition

1).All nucleated cells have major MHCI proteins on Adaptive immunity,acquired immunity their surfaces.

2). Dendritic cells and macrophages (antigen presenting cells) also have MHCII on their surfaces. They phagocytize pathogens, they digest and present pieces of the foreign peptides on their surface by MHCII proteins to Adaptive immunity,acquired immunity T cells that have the proper antigen receptor.

3).T helper (TH) cells are activated by antigen present by MHCII from antigen-presenting cells.

4). Cytotoxic (killer ) T (TC) cells are activated by antigen Adaptive immunity,acquired immunity-presented by MHCI – cells infected by virus, intracellular bacterial pathogens, transformed cancer cells, or foreign tissues (organ transplant).

5). Macrophages that have processed an antigen secrete lymphokine interleukin-1 (IL-1), which activates Adaptive immunity,acquired immunity T helper cells, in turn, ^ T help cells secrete lymphokines such as interleukin-2 (IL-2) and gamma interferon.

6). IL-1 from macrophages and IL-2 from T helper cells activate B cells to make antibody and other Adaptive immunity,acquired immunity T cells, such as cytotoxic (killer) T (TC) cells and memory cells.

7). TC cells can be recognized by a CD8 glycoprotein on their membrane. T helper cells can be recognized by a CD Adaptive immunity,acquired immunity4 glycoprotein on their membrane.

8). IL-1, Il-2 and gamma interferon together cause undifferentiated cells to become natural killer (NK) cells.

Processed antigens on MHC class II molecules bind with T Adaptive immunity,acquired immunity cell receptors. Next, IL-1 secreted from macrophages and IL-2 secreted from T helper cells activate the T helper cells, which can then differentiate into TH1 cells and TH2 cells.

Certain pathogenic bacteria Adaptive immunity,acquired immunity can grow in macrophages after they have been phagocytized. TH1 cells can release γ-interferon, a cytokine that causes such infected macrophages to become resensitized to other T cells – cell-mediated immunity.

TH2 can Adaptive immunity,acquired immunity activated B cell to produce antibody – humoral immunity.

AIDS destroys TH cells, thereby impairing both humoral and cell-mediated immunity.


Virus-infected cell

Bacteria-infected cell

Cellular location of antigen


Within phagosome

Displaying MHC molecules

Class I

Class II

T Adaptive immunity,acquired immunity cell involved

Killer T cells, TC or CD8 T cells

Helper T cells, TH or CD4 cells

Action of T cell

Kills the infected cell

Stimulate the infected cell to kill bacteria in its pagosome.

^ How Adaptive immunity,acquired immunity Killer Cells Kill

TC and NK cells destroy target cells by releasing the lethal protein perforin. Peforins bores holes in the target cell membranes, so that essential molecules leak out and the cells die Adaptive immunity,acquired immunity.

The Role of activated Macrophages

Certain pathogenic bacteria can grow in macrophages after phagocytosis, such as those that cause tuberculosis, leprosy. The lymphokine macrophage activating factor helps stimulate antimicrobial processes by increasing Adaptive immunity,acquired immunity production of hydrogen peroxideand other enzymes to kill the organismsWhen macrophages fails to kill pathogens, the pathogens are walled off in granulomas.


Such as staphylococcal toxins that cause food poisoning, can bind Adaptive immunity,acquired immunity to MHCII molecules and T cells but does not involve specificity.

The superantigens binds to T cells with different specificities, it is polyclonal.

This activates T cells at up to 100 times the normal rate Adaptive immunity,acquired immunity and then secrete immense amounts of IL-2. The excess IL-2 gets to the blood stream, and cause nausea, vomiting, fever, malaise and symptoms of shock.


Host defense Adaptive immunity,acquired immunity in healthy adults in an unpolluted environment prevent nearly all infectious diseases. Individuals with reduced resistance are called compromised host.

Factors that reduce host resistance include very young or old age, stress, seasonal Adaptive immunity,acquired immunity patterns, poor nutrition, traumatic injury, pollution, and radiation. Complement deficiencies, immunosuppressants, infections such as HIV, and genetic defects impair immune system function.


Capsule: inhibits macrophages recognition and phagocytosis

Microbe can inhibit Adaptive immunity,acquired immunity lysis within macrophage

Microbe can force non-immune cells to phagocytizeprovides protection to microbe

Exoenzymes / exotoxins

Leukocidin: kills white blood cells

Hyaluronidases: destroys hysluronic acid, the connective tissue binding host cells


Use Adaptive immunity,acquired immunity host proteins :eg. Staphylococcus aureus has protein A on its wall. Interacts

Protein A + IgG causes IgG reactive part to point away from bacteria neutralizes


Change antigenic appearance: forces immune system to react Adaptive immunity,acquired immunity to each other new serotype


Exoenzymes: Collaginase/Lecithinasegangrene

Hemolysins: kill red blood cells

Lipase, nucleases: destroy tissues

Exotoxins: secreted, potent, against a specific chemical reaction in host

Can be used to create Toxoids (antitoxin)

Eg Adaptive immunity,acquired immunity. Botulism & Tetanus toxin block nerve transmission

Diptheria inhibits translation

Endotoxins: in cell wall, not highly potent, general effects, highly resistant to heat

^ Immune Tolerance

Immune tolerance is lack of response to the body’s own constituents Adaptive immunity,acquired immunity.

One basis of immune tolerance is clonal deletion: differentiating immune cells are killed by antigens, Cells that react against the body’s own constituents are eliminated.

The body alos has mechanisms to Adaptive immunity,acquired immunity destroy fully mature immune cells if they act against the body’s constituents.


Active Immunization

^ Active immunization induces the same response as the one that occurs during a disease. Immunization chanllenges the Adaptive immunity,acquired immunity immune system to develop specific defense and memory cells.

Active immunization is conferred by vaccines and toxiods. Vaccines can be мейд from live, attenuated organisms, dead organisms, part of organisms, or a toxoid Adaptive immunity,acquired immunity. Toxoids are мейд by inactivating toxins.

The recommended immunizations for healthy infants and children in the United States are summarized in Table 17.8

The benefits of active immunization against life-threatening diseases nearly always Adaptive immunity,acquired immunity outweigh the hazards. Reactions to vaccines can cause serious side effect, but their incidence is lower than the incidences of the diseases themselves.

^ Vaccines мейд with live organisms offer longer-lasting Adaptive immunity,acquired immunity immunity than those мейд with dead organisms, parts of organisms or toxoids.

Measles (both rubella and rubeola) vaccines and oral poliomyelitis vaccine, which contain live viruses has life time immunity.

Intramuscular polio vaccines, which Adaptive immunity,acquired immunity contains killed viruses and typhoid fever vaccines which contains dead bacteria, confer immunity that lasts 3 to 5 years.

^ Tetanus and diphtheria toxoids confer immunity of about 10 years’ duration.

Recommend Immunization

Three vaccines that Adaptive immunity,acquired immunity immunize against seven diseases are recommended in the U.S. for routine immunization of infants and children.

1.DTaP vaccine contains Diphtheria toxoid, Tetanus toxoid, and

accellular Pertusis (whooping cough) bacteria,

2.Poliomyelitis Adaptive immunity,acquired immunity vaccine

a). The Sabin: contains three different types of live polioviruses

b). The Salk: contains killed virus.

^ 3.MMR vacicine contains live rubella, rubeola, and mumps viruses.

4. Hib vaccines contains Haemophilus influenzae, type b Adaptive immunity,acquired immunity of causing meningitis.

5. BCG (Bacille Calmette-Guerin) vaccine to protect against tuberculosis in underdeveloped countries.

6. Hepatis B vaccine.

Passive Immunization

Passive immunization occurs by the same mechanism as natural passive transfer antibodies.

Passive immunity is conferred Adaptive immunity,acquired immunity by antisera such as immune serum globulin (gamma globulin), hyperimmune or convalescent sera, and antitoxins.

The benefits of passive immunization are limited to providing only temporary protection; the side effects are Adaptive immunity,acquired immunity mainly allergic nature.

^ Future of Immunization

Subunit vaccines produce fewer side effects than whole cell killed vaccines and offer greater safety than do attenuated vaccines.

Recombinant DNA vaccines contain genes for antigens of Adaptive immunity,acquired immunity pathogens inserted into nonpathogenic organisms’ genomes and are very safe.



Antibodies produced by plasma cells are the chief immunological defense against bacterial antigens. Most immune Adaptive immunity,acquired immunity responses to bacteria serve to promote phagocytosis of the invading cells.


Viral infections is combated by nonspecific defenses, interferon, and antibodies. In addition, the TC cells of cell-mediated responses and NK cells are Adaptive immunity,acquired immunity important in destroying virus-infected cells.


Immune response to fungi involve IgA antibodies and are primarily cell-mediated.

Protozoa and Helminths

Immune responses to parasite protozoa and helminthes are largely cell Adaptive immunity,acquired immunity-mediated. T cells release cytokines that activate macrophages and attract other leukocytes. Allergic reactions to helminthes can be more damaging to the host than to the parasites.