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Developments in biotechnology in recent years have enabled the discovery of new pharmacological agents for the treatment and prophylaxis of infectious diseases. The agents obtained from these biotechnological procedures possess specific characteristics which significantly distinguish them from drugs obtained by chemical synthesis. These properties cover the entire development process, from investigation and production up to their administration to patients. The pharmokinetics of these preparations influence their administration routes and dosage regimens. The discovery of these drugs has led to major advances in the treatment and prophylaxis of infectious processes which until very recently had no effective treatment. The investigation and production of these drugs requires the use of highly technical resources resulting in high costs and therefore a more expensive drug on the market compared to other drugs. Nevertheless, well documented pharmoeconomic studies show that the use of this type of drug for certain symptoms may be highly cost effective. This article includes some of the possible applications of biotechnology in the infectious disease field, although the current situation indicates that more detailed and broader applications may be elaborated on in ensuing issues. The future of these drugs in chemical therapy for the treatment and prophylaxis of infectious diseases is exceedingly promising and many of these drugs are currently under laboratory investigation, more so than those under development from a chemical synthesis approach.

Although there are several immunological mechanisms to eliminate the intracellular pathogens, they have elaborated a variety of strategies to escape of the immune response and to make possible their survival and replication in the host. Some parasites modulate the production of several toxic molecules synthesized by the immune system. Several parasites are highly sensitive to nitric oxide (ON) and their derivatives. ON is produced in macrophages (Mphi) after stimulation with microbial products or cytokines. In the past, Mphi were defined as inflammatory cells (classically activated Mphi), able to produce inflammatory mediators, to act like antigens presenting cells and to kill intracellular pathogens. Nevertheless, activated Mphi involve a more heterogeneous group of cells with different biological markers that can carry out different immunological functions. Alternatively activated Mphi fail to produce ON due to the arginase induction and consequently they have diminished their capacity to kill intracellular pathogens. It has been reported the induction of arginase by different parasites; therefore this mechanism could favor their survival in the host. In our group, we studied the participation of arginase in a model of Trypanosoma cruzi infection and the intracellular signals involved in the replication of this parasite in Mphi. The data obtained from our works would allow the understanding of some mechanisms by which cells can be programmed to favor the establishment of chronic parasitic infections.

The immune system is a tight network of different types of cells and molecules. The coordinated action of these elements mounts a precise immune response against tumor cells. However, these cells present several escape mechanisms, leading to tumor progression. This paper shows several cellular and molecular events involved in the regulation of the immune response against tumor cells. The interaction of several molecules such as MHC, TcR, adhesins, tumor antigens and cytokines are discussed, as well as the most recent knowledge about escape mechanisms and immunotherapy.

General aspects on the immune response to poliovirus are described, considering it's molecular structure. Since the poliovirus is a cytocide agent, antibody immune response is the most important among those related to protection; however probably a minimum of helper T cells are required (more than 200 T lymphocytes with phenotype CD4) in order to get a best response. Phagocyte, NK cells and T lymphocytes probably take part in the viral clearance from the central nervous system, also in the host injure mechanisms. Some molecular aspects of the neutralizing antibodies combining site are described too. Activation particularities, of the common mucosal immune system confirm the importance of the secretory immune response in the control of the poliomyelitis.