DIFFERENTIAL EXPRESSION OF NERVE GROWTH-FACTOR IN LEISHMANIA-MAJOR MURINE CUTANEOUS LEISHMANIASIS

The cross-talk between the immune and nervous systems is becoming an i nteresting field of research and there is accumulating evidence suppor ting this notion. In the present study,ve investigated the levels of n erve growth factor in a murine model of cutaneous leishmaniasis, using a two-site ELISA. Two strains of inbred mice were used for this purpo se, namely BALB/c and C57BL/6, genetically susceptible and resistant, respectively, to infection with Leishmania major. This work demonstrat es a difference in expression of nerve growth factor in the skin and s econdary lymphoid organ microenvironment, as well as in the serum, bet ween these mouse strains. The high nerve growth factor levels in the m icroenvironment seem to be important and possibly critical for the out come of the disease: Compared with controls, the resistant strain, C57 BL/6, expressed significantly increased nerve growth factor levels in the skin, secondary lymphoid organs and serum at 1 week post-infection , whereas the susceptible strain, BALB/c, showed no change in the skin and a slight increase in the lymphoid organs and serum at this time-p oint. These high nerve growth factor levels in the early stage of the disease, whether produced directly by the inflammatory cells or indire ctly through its induction by other cytokines or both, might indicate a contribution of this neurotrophic factor to differentiation of naive T lymphocytes into either Th, or Th, subsets that fundamentally gover n the disease outcome. The expression of significantly elevated nerve growth factor levels in the skin and lymphoid organs of C57BL/6 at the late studied time points might suggest a role for nerve growth factor in the resolution of the disease process, which is usually evident fr om 6 weeks post-infection in this model. The high nerve growth factor levels expressed in the skin, lymph nodes and serum of BALB/c at late stages of the disease may be explained as an attempt to counteract the progression and dissemination of the disease. This investigation adds further experimental evidence for an anti-inflammatory effect of nerv e growth factor, possibly through its action as a link between the ner vous and immune systems.