Agglutination Reactions

Agglutination is defined as the antigen-antibody reaction in which antibodies cross-link particulate antigens resulting in the visible clumping of particles. Antibodies that show such reactions are called agglutinins.

Agglutination reactions work on the principle of cross-linking of the polyvalent antigens. Following are the advantages of agglutination reactions: 

  1. easy to perform 
  2. require no expensive equipment, and 
  3. detects antibody concentrations as low as nanograms per milliliter. 

Types of agglutination reactions: 

  1. Hemagglutination:
    type of agglutination reaction is routinely performed to type red blood cells (RBCs), wherein RBCs are mixed with antisera to the A or B blood-group antigens on a slide. The presence of antigen on the cell surface is proved by forming a visible clump on the slide. This RBC typing forms the basis for matching blood types for transfusions.
  2. Bacterial Agglutination:

This type of agglutination reaction is performed to diagnose infection and provide a way to type bacteria. Any bacterial infection elicits the production of serum antibodies within the host. 

These serum antibodies are specific for surface antigens on the bacterial cells, which bacterial agglutination reactions can detect.

Bacteria is added to the previously serial diluted array of tubes containing serum from a patient thought to be infected with a given bacterium. The last tube, which shows visible agglutination, reflects the serum antibody titre of the patient. Thus, the agglutinin titre is the reciprocal of the greatest serum dilution that elicits a positive agglutination reaction.

  1. Active agglutination 

In this type of agglutination, epitopes of interest are naturally found on a test particle, such as antigens found on RBCs, bacterial and fungal cells.


Examples –

  1. Blood grouping and cross-matching
  2. Widal test for diagnosis of typhoid fever 
  3. Brucella agglutination test for Brucellosis 
  4. Weil Felix test for Rickettsiosis
  5. Passive agglutination: 

Passive agglutination is useful when the epitope of interest does not occur naturally on the cells or particles to be agglutinated. The epitopes or soluble antigens are chemically fixed to carrier particles such as – latex, polystyrene, bentonite.

 Passive agglutination is also useful when pathogen culture is not feasible, e.g., viral diseases. 

Synthetic beads offer better consistency, uniformity, and stability. In addition, those agglutination reactions which employ synthetic beads are rapidly read within 3 to 5 minutes of mixing the beads with the test sample.  




  1. Cellular and Molecular Immunology by Abul K. Abbas – 7thEdition 
  2. Kuby Immunology – 5thEdition 


Synonym: Localized Anaphylaxis 


Atopy is defined as the tendency of an individual to produce IgE antibodies in response to various environmental antigens and thus develop strong immediate hypersensitivity (allergic) responses. Individuals with allergies to environmental antigens (e.g., pollen, house dust) are atopic. 

Localized anaphylaxis involves reactions limited to a specific target tissue or organ and often involves epithelial surfaces at the site of allergen entry. Atopy is thus defined as the tendency to manifest localized anaphylactic reactions, and this tendency is inherited. 

Atopic allergies include a wide range of IgE-mediated disorders, including allergic rhinitis (hay fever), asthma, atopic dermatitis (eczema), and food allergies

Allergic Rhinitis:

This is commonly known as “hay fever” and results from the reaction of airborne allergens with the sensitized mast cells in the conjunctivae and nasal mucosa, which induces the release of pharmacologically active mediators from mast cells. The mediators thus cause localized vasodilation and increased capillary permeability. The symptoms of allergic rhinitis usually include watery exudation of the conjunctivae, upper respiratory tract and nasal mucosa, and sneezing and coughing.


Asthma, a common manifestation of localized anaphylaxis, is triggered by degranulation of mast cells with the release of mediators, but instead of occurring in the nasal mucosa, the reaction develops in the lower respiratory tract. This results in the contraction of the bronchial smooth muscles and thus eventually leads to broncho-constriction. 

Food Allergies:

A variety of foods can induce localized anaphylaxis in allergic individuals. In addition, localized smooth-muscle contraction and vasodilation can be induced by allergen cross-linking of IgE on mast cells along the upper or lower gastrointestinal tract resulting in symptoms such as vomiting or diarrhea. 

Atopic Dermatitis:

Atopic dermatitis (allergic eczema) is an inflammatory disease of the skin frequently associated with a family history of atopy. This disease is observed most commonly among young children, often developing during infancy. Serum IgE levels are often elevated, and the allergic individual develops erythematous skin eruptions filled with pus. 



  1. Cellular and Molecular Immunology by Abul K. Abbas – 7thEdition 
  2. Kuby Immunology – 5thEdition.



Immunology is the branch of science dealing with the study of immunity. Louis Pasteur is considered as the Father of Immunology.


 Immunology started from the observation of people who recovered from certain infectious diseases and who never got infected with the same.

  • The earliest written evidence on immunology is by Thucydides during 430 BC .He was describing about a plague in Athens where he mentioned that people who recovered from plague could only nurse the sick because they won’t get the disease again.
  • The first recorded attempt was by Chinese and turks in the 15 century. Dried crusts of from smallpox pustules was inhaled through nostrils or inserted into cuts in the skin. They used in this technique called variolation  to prevent the deadly and fatal smallpox.
  • Variolation technique was later improved by Edward Jenner in 1718.
  • Next major advancement was that success of Louis Pasteur in growing bacterium responsible for fowl cholera in chicken. After completing, he concluded that ageing weekend the virulence of pathogen. He called the attenuated strain as vaccine .he named it so in honor of Jenner’s technique of cowpox inoculation.
  • Next decade various researchers demonstrated that an active component from the serum of immune animals are capable neutralizing toxins, precipitating toxins and occlude rich bacteria. They were termed as angio toxin precipitating and agglutinating respectively. Gamma –globulin present in serum is responsible for this activities. This active molecule is called as antibody.


  1. Inherent Immunity

It’s a first line of defense mechanism and non-specific. Inherent immunity include physical barriers (e.g., skin, saliva etc.)and cells (e.g. Macrophages, neutrophils, basophils, mast cells etc.).It is active for first few days during infection period.

  • Adaptive Immunity

It is the second line of defense. It responds to anything that is foreign and also remembers it.It involves antibodies and lymphocytes. Active and passive immunity comes under Acquired immunity


It can be any substance that can be recognized by immunoglobulin receptor of B-cells or by the T-cell receptor when complexes with MHC. Antigens include toxins, bacteria, foreign blood and the cells of transplanted organs.


  • Exogenous Antigen: Antigens that have entered the body from outside either by inhalation, ingestion or injection .Immune response to these antigens is often sub-clinical. Some Exogenous Antigen later become endogenous Antigens.
  • Endogenous Antigens: They are generated within an individual normal cells as a result of cell metabolism. Endogenous antigens include xenogenic, autologous and idiotypic antigens.
  • Tumour Antigens: They are present on the surface of tumor cells. They can sometimes be presented only by tumour cells and never by the normal ones due to some tumour specific mutations, such antigens are called Tumour specific Antigens (TSAs).Commonly these antigens are presented by both tumour cells and normal cells, and they are called Tumour Associated Antigens.



They are group of glycoproteins which are present in the serum and tissue fluids of all mammals. They are produced by the immunocompetent B-cells called as plasma cells .Some of these antigen-binding proteins are carried on the surface of B-cells, where they act as receptors for specific antigens and thus, confers antigenic specificity on B-cells.

Structure of Antibodies: It is Y-shaped in appearance whose arms can swing at an angle of 180 degree. It consist of two identical light chains and heavy chains which are linked by disulphide bonds and non-covalent interactions such as hydrogen bonds, salt bridges and hydrophobic bonds in the form of heterodimer.


  • Immunoglobulin G (IgG): It is a major immunoglobulin present in serum. It is the major Ig produced during the secondary response. It is the only Ig which can cross placenta. It also helps in the activation of classical compliment pathway.
  • Immunoglobulin A (IgM): It accounts for approximately 5%-10% of the total serum immunoglobulin with an average serum concentration of 1.5 mg/mL is the first immunoglobulin to be synthesized by the newborn. It is confined to the intravascular pool only. IgM are capable of agglutinating the antigen as well as it can neutralize the viral particles.IgM is also more efficient activator of the classical complement pathway.
  • Immunoglobulin a (IgA): It constitutes only 10%-15% of the total immunoglobulin in serum. It served as a first line of defense against the microbial invasion at the mucosal surfaces. Secretory IgA present in breast milk protect the newborn against infection during the first month of life.
  • Immunoglobulin E (IgE): It’s present in extremely low in serum. It mediate the immediate hypersensitivity reactions or allergic reactions. On the exposure of allergen, IgE will be produced which binds to Fc receptors present on the membranes of blood basophils and tissue mast cells. It also plays a major role in parasitic infections
  • Immunoglobulin D (IgD): It constitutes only 0.2% of the total immunoglobulin in serum. It is expressed by mature B-cells on its surface together with IgM.


Immunology is a diverse and growing discipline. It plays an important role in the development vaccines. Immunology is associated with the treatment of allergy and asthma. It plays a major role in the disciplines of medicine especially for organ transplantation, oncology, virology, bacteriology. Immunoinformatics is special stream which link immunology and bioinformatics.Majorily for vaccine design.


Immunology: Immune System

And Its Type


  • About
  • Immune system
  • Immunity
  • Types of immunity
  • Innate immunity
  • Acquired immunity


  • Immunology refers to the branch of biology that deals with the study of immune system in all organisms.
  • Any malfunction in this system lead to the diseases like autoimmune disease, hypersensitivity, transplant rejection and immune deficiency.
  • The term was given by Ilya Ilyich Mechnikov and received noble in 1908 for his work. He studied on the larvae of starfish, pinned thorns into the larvae and found unusual cells surrounds the thorns. This was the active response by the larvae. Mechnikov was the first to observe phagocytosis.

Immune system:

  • A different type of cells and molecules which protects our body from pathogens is collectively called immune system.
  • Pathogens may be anything from algae, fungi, bacteria to haptens (molecules that may cause an immune response).
  • The cells and molecules of the immune system were distributed all over the tissue of the body which plays role in elimination or prevention from pathogens.


  • Immunity is the ability of organism to protect itself from the disease causing organism.
  • Our body regularly comes in the contact of numerous pathogens but we few results into disease the reason is that our body develops antibody against the pathogen and protect from the disease.


  • Innate immunity
  • Acquired immunity

Innate immunity:

  • Innate immunity is the type of immunity with which the individual is born.
  • It serve as the first line of defence an provided various components like skin, mucus membrane phagocytic cells.
  • The mechanisms of innate immunity are anatomical barrier, physicochemical barrier, phagocytic barrier and inflammation.

Types :

Species immunity: one species are resistance but other are susceptible to the same infection. Example, birds are resistant to the anthrax but human doesn’t.

Racial immunity: one race is susceptible other is more resistant to same infection. Example, certain African race are resistant to malaria but Asian or Americans are susceptible.

Individual immunity: to a certain infection the individual of race or cast is resistant but other individual of same race is susceptible to the same infection.

Acquired immunity:

  • The immunity which the individual get during its life span after each microbial infection is called acquired immunity. Example is an individual was ever infected by any infection like chicken pox virus he/ she become life time resistant to chicken pox.
  • Antibodies and t-lymphocytes contribute in acquired immunity.
  • The t-cells and antibodies are specific to the pathogen hence acquired immunity is also known as specific immunity.


Active immunity

  • The active immunity is the condition when the host itself produces antibodies.

There are two types of active immunity

Artificial – by vaccination

Natural – by natural infection

Passive immunity

The condition in which the host doesn’t produces antibodies itself but antibodies developed in other host cell provides immunity known as passive immunity.

Two types:

Artificial – antibody introduced in the host body for immunity

Natural – antibody from the mother to foetus.


Antibodies are the immunoglobulin found in the blood and serve as protection against substance like antigen.

Antigens are the protein or carbohydrate which activates the immune system.

There are 5 types of antibodies- IgA, IgM, IgG, IgE and IgD.