Introduction

Immunity is a significant and flexible defence mechanism in the body that protects from pathogens and microorganisms. It prevents disease-causing organisms from attacking and depleting the body’s normal functions. The body’s immunity has an ability to synthesize a wide range of molecules that can recognize and eliminate any foreign organisms (Richard, 2003). Immunomodulation is not a new term that is evolved recently in medicine. It had been in practice from late 1800 till today. The use of vaccines was the general method to modulate immunity in human beings. The term immunomodulation reminds few scientists names like Louis Pasteur, Jonas Salk, Edward Jenner and Emil von Behring. Vaccines involve the process of invoking the body’s natural immune system. Artificially generated antigens or weakened or attenuated disease causing microorganisms are used to target and provoke the synthesis of antibodies against a specific antigen. This provocation induces the needed defence mechanism in the body and is a huge milestone in immunomodulation. Immunomodulation is defined as alteration (increase/decrease) of the immune response of the body to antigens. Any enhancement or stimulation in the immunity is called as immune-stimulation, and lowering of the immune response of the sensitivity is termed as immune-suppression. The core concept of the immunomodulation lies in alteration of immunity by any agent that causes disease or toxicity but at a varied dose and time.

Need for Immunomodulation

Immune suppression is usually applied in the following cases.

• To suppress the transplant rejection after organ or tissue transplantation (Heart, Kidney, Liver, Skin etc.).

• To limit the GVHD (Graft v/s Host Disease) after bone marrow transplantation.

• To suppress elevated immunity in autoimmune disorders like Myasthenia gravis, SLE, RA and Psoriasis.

• To suppress selectively the Rh of the hemolytic disease of the newborn babies.

Immune-stimulation is needed when the immune system of the host is inactive or impaired. This is a therapeutically needed in the conditions with infections, disease and prophylactically need in the period post-surgery to prevent opportunistic infections.

Materials and Methods

Screening of immunomodulatory activity

There are various methods by which a herbal extract or a drug can be screened for the immunomodulatory activity. In general, there are two classes of screening methods. They are in vivo and in vitro evaluation. Usually, in vivo evaluation employs Rats or any other higher animals for screening. There are different methods to estimate the activity in animals by measuring various body tissues analysis. The analyses were made by inducing the hypersensitivity or allergens into the animal body, followed by the drug administration and examined for the activity. The following are the induction methods and estimation types of immunomodulation.

Transplantation

Induction of the allogenic transplant rejection and GVHD (Graft v/s Host Disease) determination.

Thyroidal induction

Experimental induction of autoimmune thyroiditis and hypersensitivity in the thyroid.

Arthritis estimation

Induction of adjuvant arthritis, induction of reversed passive arthritis, progressive arthritis induced by proteoglycans and arthritis induced by collagen type II.

Skin and nerves related

Cutaneous passive anaphylaxis method, MRL/IPR strain mice to test SLE and experimentally induced myasthenia gravis.

Hypersensitivities

Systemic induction of anaphylaxis, immediate hypersensitivity of Arthus type, induction of delayed hypersensitivity and Schultz-Dale reactions.

Other Systems

Induction of glomerulonephritis by anti basement membrane antibody, induction of autoimmune myocarditis by porcine cardiac myosin and myocarditis induced by coxsackievirus.

As there is raising concern for the testing and treatment of animals in the laboratories, the use of animals is slowly replaced by simulation software and in vitro procedures. The following parameters are evaluated when doing in vitro evaluation. They are,

• In vitro Plaque Forming Colonies (PFC test).

• Estimation of the histamine inhibition release that occurs in mast cells.

• Estimation of the enzyme DOD (Dihydro-orotate dehydrogenase).

• Estimation of the proliferation of lymphocytes that is induced by Mitogen.

• Determination of the chemiluminescence in the macrophages.

• Estimation of Inhibition of the proliferation of T cells.

Herbal investigations

There are synthetic drugs that have potent immuno modulatory activity but are not devoid of side effects. Few of them include Alopecia, Lung toxicity, Lymphoma, Nephrotoxicity, Hepatic fibrosis, Seizures, Hirsutism, etc. (Kremer, 1994). Immunomodulation has been adopted in the traditional systems of medicine like Ayurveda, in which the concept of rasayana has most prominence. Various plants have been studied as rasayana drugs in Ayurveda and other Indian systems of medicines. Immunomodulatory activity of various plants had been used for their immunoadjuvant activity, antirheumatic activity, antiageing property, anticancer and adaptogenic activity. This folklore and scientific activity in this field had a holistic and innovative approach for the discovery of powerful lead molecules and affordable drugs. The medicinal plants and herbs are known to be safer and better alternatives.

Phytomedicine gained its importance recently in this arena and this article is one of the attempts to review the immunomodulatory plants that have been investigated for activity after 2010.

Conclusions

Medicinal plants and natural drugs are used as potent sources of immunomodulation and contributors for the derivation of the leads responsible for the development of immunomodulatory agents. The drug discovery and isolation of those leads from the herbal origin are more specific in the chemotherapy. Apart from the advantages of the herbal medicines in view of their safety and potency, the limitations for the use of herbs concerning their variations in the quantity of chemical constituents had to be addressed. The inconsistency of the in vivo response with the phytochemicals is also a limiting step for their effective usage as immunomodulatory agents. Overall, herbs had been supplying the chemical constituents that can be used directly or in the purified form as immunomodulatory agents.