Mycoplasma mycoides subsp SC (Mmm Sc) is a small bacteria of the Genus Mollicutes, responsible for Contagious Bovine Pleuropneumoniae (CBPP), an OIE listed infectious disease characterised by low mortality and high morbidity. From the economical point of view and in endemic areas such as Asia and Africa CBPP represents a crucial problem. Acute pulmonary lesions, typical of the disease, induce severe respiratory distress leading to death in some cases. The majority of infected animals develop chronic lesions responsible for loss of production and fertility. Vaccines currently used in the attempt to control CBPP spread are based on subcutaneous injection of partially attenuated strains of Mmm Sc. These vaccines confer only a short time protection (less than one year) and present residual virulence sometimes responsible for strong inflammatory reaction at the site of vaccination and invasive oedema. In some cases reversion to virulence of vaccine strain represented the cause of new CBPP outbreaks following vaccination. The drawback associated to the actual vaccination strategy dictate the need for development of safer and more effective vaccines such as "sub-unit vaccines", which are based on the selection of specific protein fraction of the pathogen with antigenic activity. To achieve these objectives a better knowledge of surface, secreted and pathogenic molecules from Mycoplasma is required. Investigation should also be directed to clarify the pathogenic mechanisms of CBPP and the role of the cellular and humoral components of the immune system during infection. Other studies (Jores et al 2008) and a recent experiment of in vivo lymphocyte depletion (unpublished data) question the correlation of CD4+ T cekksm IFN-y secretion and disease severity, leading to the idea that acquired immunity may play a marginal role during the inflammatory process.