Plant immunization

Plant immunization is the process of activating natural defense system present in plant induced by biotic or abiotic factors. Plants are pre-treated with inducing agents stimulate plant defense responses that form chemical or physical barriers that are used against the pathogen invasion. Inducers used usually give the signals to rouse the plant defense genes ultimately resulting into induced systemic resistance. In many plant-pathogen interactions, R-Avr gene interactions results in localized acquired resistance or hypersensitive response and at distal ends of plant, a broad spectrum resistance is induced known as systemic acquired resistance (SAR). Various biotic or abiotic factors induce systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Some of the biotic or abiotic determinants induce systemic resistance in plants through salicylic acid (SA) dependent SAR pathway, others require jasmonic acid (JA) or ethylene. Host plant remains in induced condition for a period of time, and upon challenge inoculation, resistance responses are accelerated and enhanced. Induced systemic resistance (ISR) is effective under field conditions and offers a natural mechanism for biological control of plant disease.     

More effective immunization

Immunization activities, in spite of being one of the easiest health components to deliver, are frequently forgotten or relegated to a low priority. One of the major reasons why immunization services have not been more widely implemented in developing countries is that present knowledge is inadequately applied. Although gaps do exist in some technical and operational areas, the most important concern is the application on a larger scale of already available knowledge and technologies. It is emphasized that programming strategies should promote delivery of immunization services to the population groups at highest risk of contracting the target diseases--children less than 1 year old and pregnant women--and that these services can most effectively be delivered as an integral part of the primary health care system. The use of immunization coverage as a simple and meaningful indicator of the extension of coverage of health services is analysed by using data from immunization programmes in two countries of the Americas.     

Resistance to immunization

Despite a well documented efficacy and a generally good adhesion of a large majority of the lay population and health care professionals as well, immunization is still the object of controversies. It affects several vaccines against hepatitis B, influenza, BCG, pertussis and measles. In most cases, polemics on vaccination result from a temporal association between a vaccination and the revelation of a serious disease, when the immunization is performed at the peak of incidence of the disease. Controversies can also be initiated by scientific publications, even though these are often biased, by a misinterpretation or the absence of official positions from the health care authorities, or by justice decisions, whose criteria differ from the scientists' ones and are therefore difficult to understand for the lay public. Furthermore, the scientific demonstration of the exclusion of a risk is difficult to obtain. In the past, it appeared to be very difficult to stop controversies. Improving the communication is the main issue, towards lay public as well as health care professionals. This implies to learn how to better use the media, to motivate and educate professionals who administer vaccine, and anticipate the eventuality of a temporal relationship between vaccination and occurrence of a serious disease by an improved management of the pharmacovigilance system.     

Nonspecific photophysiological immunization]

A hypothesis is suggested on the positive effect of light radiation on the formation of protective immune mechanism related to the photophysiological destruction of porphyrins. References to experimental data are given which illustrate the possibility for existence of such a mechanism.     

Genetic immunization of neonates

The vaccination of neonates is generally difficult due to immaturity of the immune system, higher susceptibility to tolerance and potential negative interference of maternal antibodies. Studies carried out in rodents and non-human primates showed that plasmid vaccines expressing microbial antigens, rather than inducing tolerance, triggered significant humoral and cellular immunity with a Th1 component. The ability of bacterial CpG motifs to activate immature antigen-presenting cells is critical for the neonatal immunogenicity of DNA vaccines. In addition, the endogenous production of antigen subsequent to transfection of antigen-presenting cells may explain the lack of inhibition by maternal antibodies of cellular responses. Together, these features make the plasmid vaccines an appealing strategy to prime immune responses against foreign pathogens, during early life. In combination with subsequent boosting using conventional vaccines, DNA vaccine-based regimens may provide a qualitatively superior immunity against microbes. Thorough understanding of immunomodulatory properties of plasmid-vectors may extend their use for early prophylaxis of inflammatory disorders.     

Simultaneous immunization against tuberculosis

Background

BCG, the only licensed vaccine against tuberculosis, provides some protection against disseminated disease in infants but has little effect on prevention of adult pulmonary disease. Newer parenteral immunization prime boost regimes may provide improved protection in experimental animal models but are unproven in man so that there remains a need for new and improved immunization strategies.

Methods and Findings

Mice were immunized parenterally, intranasally or simultaneously by both routes with BCG or recombinant mycobacterial antigens plus appropriate adjuvants. They were challenged with Mycobacterium tuberculosis (Mtb) and the kinetics of Mtb growth in the lungs measured. We show that simultaneous immunization (SIM) of mice by the intranasal and parenteral routes is highly effective in increasing protection over parenteral BCG administration alone. Intranasal immunization induces local pulmonary immunity capable of inhibiting the growth of Mtb in the early phase (the first week) of infection, while parenteral immunization has a later effect on Mtb growth. Importantly, these two effects are additive and do not depend on priming and boosting the immune response. The best SIM regimes reduce lung Mtb load by up to 2 logs more than BCG given by either route alone.

Conclusions

These data establish SIM as a novel and highly effective immunization strategy for Mtb that could be carried out at a single clinic visit. The efficacy of SIM does not depend on priming and boosting an immune response, but SIM is complementary to prime boost strategies and might be combined with them.