Adjuvants

In simple words adjuvant means something that assist or aids and in terms of immunology adjuvant is defined as any substance that helps to accelerate, prolong, or enhance the antigen-specific immune responses when combined with specific vaccine antigens . Adjuvants help to increase the immune response to vaccines or Immuno therapies.

Types Of Adjuvants

There are several types of Adjuvants depending upon their structure , contents inside them , function they perform etc . These are the classification of some of the Adjuvants :

• Mineral Salt Adjuvants :

These types of adjuvants mainly comprise the aluminium hydroxide and phosphate adjuvants as well as calcium phosphate adjuvants .

Examples :

Aluminium phosphate

Calcium phosphate

Magnesium hydroxide

• Oil-in-Water Emulsions :

These types of Adjuvants consist of squalene as the oil and the antigens mixed in the outer water , forming an oil in water emulsion and stimulate a strong immune response .

Examples :

Freund's adjuvant

MF59

AS03

• Saponin Adjuvants :

Saponins can stimulate the release of cytokines and chemokines during the immune response , they also regulate immune cell recruitment and helps in intracellular signaling mechanisms . As they have the ability to activate immune system hence they are categorised as Adjuvants .

Examples :

Quil A : It is a saponin mixture extracted from the bark of the South American tree called Quillaja saponaria Molina .

Iscomatrix

• Polysaccharide and Liposome Adjuvants :

Dextran , Chitin , Chitosan are some of the examples of polysaccharide Adjuvants where as Liposomal formulations such as virosomes and Cationic lipids like DOTAP are examples of liposome Adjuvants .

• Cytokine Adjuvants :

Various cytokines have been shown to be effective immunological adjuvants as they enhance protection induced by viral , bacterial or parasitic vaccines .

Some examples of these types of Adjuvants are :

Interleukin-2 (IL-2)

Interferon-gamma (IFN-γ)

Granulocyte-macrophage colony-stimulating factor in short GM-CSF

• Other Adjuvants :

There are some Bacterial Derivative Adjuvants such as Lipopolysaccharides , Muramyl dipeptide and Outer membrane vesicles (OMVs) .

Synthetic Adjuvants include Polyethyleneimine , Poly-L-lysine and Polylactic-co-glycolic acid in short PLGA .

Some Natural Adjuvants are also present in nature like Yeast-derived beta-glucans , Mushroom derived beta-glucans and Plant-derived saponins .

Mechanism Of Action :

Adjuvants enhance immune responses through various mechanisms which are explained below :

• Depot Formation In which Slow release of Antigen takes place . Then Prolonged exposure to immune cells occur .

Examples : Aluminium salts and oil-in-water emulsions Adjuvant.

• Immunopotentiating Complexes helps to enhance antigen presentation by activating immune cells such as dendritic cells , and T-cells

Examples: Saponins like Quil A and QS-21 and liposomes Adjuvants .

• Immunostimulation :

In this mechanism Activate pattern recognition receptors or PRRs helps to Induce cytokine production such as pro-inflammatory or Th1/Th2 .

Examples : CpG motifs , bacterial derivatives like LPS and MDP

• Antigen Delivery : In this method it targets specific cells or tissues and enhance antigen uptake and processing .

Examples: Liposomes , nanoparticles , virosomes etc

• Activation of Immune Cells occur through Dendritic cell maturation and activation . It also helps in T-cell activation and proliferation . Activation of B-cell and antibody production takes place .

Examples: Cytokines and immunostimulatory sequences Adjuvants .

• Modulation of Immune Responses :

It Balance Th1/Th2 responses and induce tolerance or immune suppression .

Examples : Glucocorticoids, immunosuppressive cytokines etc

Applications Of Adjuvants :

• Vaccines : It is used in vaccine like

Influenza vaccines such as Fluad, Fluzone .

HPV vaccines including Cervarix and Gardasil

Hepatitis B vaccines like Recombivax

Pneumococcal conjugate vaccines such as Prevnar 13 and Meningococcal conjugate vaccines like Menactra .

• Adjuvants are also used in immuno therapy against many diseases .

Examples :

In Cancer treatment it acts as checkpoint inhibitor .

During Allergy treatment such as allergen immunotherapy

In Autoimmune disease treatment like rheumatoid arthritis etc

• Diagnostic Assays : Adjuvants helps in diagnosis of many disease as it is used in

ELISA or enzyme-linked immunosorbent assay .

Western blotting , Immunohistochemistry and Flow cytometry etc

• Research Applications : It plays important role in research applications such as Immunology research , Cancer research Infectious disease research and Vaccine development .

• Cosmetic and Dermatological Applications : Apart from having various immunological applications it also helps in Skin immunotherapy , Hair loss treatment and Anti-aging treatments which enhances the outer beauty .

• Others : It helps in Food allergy treatment Environmental allergy treatment and also in Asthma treatment . It helps in cancer treatment by Immunomodulatory therapies such as IL-2 and IFN-γ .It is used in Adoptive T-cell therapy , Gene therapy by Enhancing gene expression and Improving gene delivery .

Haptens

“ Haptens ” came from a Greek word “haptein” which means to fasten . This term was 1st given by Karl Landsteiner .These are small , non biological molecules that binds to immune cells receptor but can not alone produce immune response . We can say that heptens are incomplete antigens as they lack carrier but these are non immunogenic because they can't produce immune response by their own .

Characteristics of haptens :

There are several physical , biological , immunological characters present in heptane . These characters are :

• Physical Characteristics :

These are typically Small in size and less than1,000 Dalton . These have low molecular weight and simple chemical structure . Hydrophobic or hydrophilic properties may also present in haptens .

• Immunological Characteristics :

They alone can not induce immune response hence they are Non-immunogenic but when they are attached or conjugated with a carrier protein they behave as immunogenic .

They have the ability to bind to antibodies or T-cell receptors though.

• Chemical Characteristics :

They React with functional groups like, -NH2, and -SH . Haptens form covalent bonds with carriers to become completely antigenic . They are more Stable in aqueous solutions and shows more Solubility in organic solvents .

• Biological Characteristics :

Haptens have the potentiality to cause autoimmune responses and to induce allergic reaction when combined with carriers . They Interact with biological molecules like proteins and cells . They provide metabolic stability .

Types Of Haptens :

Haptens can be classified in to several groups depending on the characteristics on which they are being separated .

• Based on Reactivity :

Based on reactivity and the nature to attract electrons they are classified in 3 groups as follows : Electrophilic haptens like dinitrophenol , Nucleophilic haptens like sulfonamides and Radical-forming haptens like all the heavy metals .

• Based on Origin :

Based on the nature of origin either they are naturally occurring or synthesised artificially haptens are classified as Natural haptens which are derived naturally from plants such as urushiol and venom from animals . Synthetic haptens like drugs or pesticides are prepared artificially and Semi-synthetic haptens are the modified natural products .

• Based on Structure :

Complex Haptens are polyvalent and precipitate with specific antibodies while simple haptens are univalent and non precipitate with specific antibodies.

• Others :

Small Molecule Haptens involve Drugs like penicillin and sulfonamides , Toxins such as diphtheria toxin , Pesticides like DDT and pollutants like heavy metals .

Peptide Haptens involve Short peptides containing 5-10 amino acids , Synthetic peptides and Tumour-associated peptides while Carbohydrate Haptens involve Sugars like glucose and galactose along with Glycoproteins and polysaccharides .

Phospholipids , Glycolipids and Steroids are examples of lipid heptens . DNA , RNA and Oligonucleotides are nucleic acid heptens while Synthetic Haptens include Dinitrophenol (DNP) , Fluorescein isothiocyanate and Isothiocyanate etc .Steroid hormones involve oestrogen and testosterone while Peptide hormones such as insulin are examples of Hormone Haptens .

Importance Of Haptens :

The importance of haptens lies in their ability to bind with specific molecules , to enhance the sensitivity during diagnosis and to induce immune responses.

Haptens are crucial in various fields due to their above mentioned unique properties :

• Immunology : Haptens help to create conjugate vaccines and facilitate understanding the immune mechanisms while also plays an important role in understanding allergic reactions.

• Medicine :

Haptens are used in ELISA , Western blot, and other diagnostic tests to detect the Antigens or disease. It also helps in Therapeutic applications by designing targeted therapies and contributes in understanding disease mechanisms .

• Pharmacology And Toxicology :

Haptens inspire development of new drugs and facilitate targeted drug delivery also aids to study drug metabolism and in understanding toxic mechanisms . Haptens help to evaluate environmental risks and inform new development of detoxification methods .

• Cancer Research :

Haptens help to identify cancer-specific markers and facilitate development of cancer vaccines and also aids in designing targeted cancer treatments.

• Environmental Science and Biotechnology :

Haptens help detect environmental pollutants like heavy metals and inform understanding of ecological toxicity also helps in developing bioremediation strategies . In biotechnology Haptens facilitate in protein designing and enables development of biosensors also plays an important role in developing bioconjugation techniques .

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