Selective tolerization of Th1-like cells after nasal administration of a cholera toxoid-LACK conjugate.

Recent reports have suggested that after infection of BALB/c mice with Leishmania major, CD4+ T cells responding to a single antigen, LACK (Leishmania homologue of receptors for activated C kinase), drive the differentiation of other responding T cells to the Th2 phenotype and so allow lesion development to occur. Transgenic mice expressing LACK in the thymus are tolerant to LACK and thus resolve infection with L. major. The oral administration of soluble protein to mice has been shown to result in the peripheral tolerance of antigen-specific CD4+ T cells. We therefore sought to tolerize LACK reactive T cells in non-transgenic BALB/c mice in order to determine the effectiveness of this tolerization approach as an alternative to standard vaccination protocols against L. major infection. Surprisingly, oral or nasal administration of up to 8 mg of recombinant LACK did not affect the outcome of infection. We therefore conjugated LACK to cholera toxin beta subunit (CTB-LACK) which has previously been shown to improve the effectiveness of oral tolerance to conjugated antigens. Nasal administration of as little as 12 microg of CTB-LACK effectively diminished the capacity of mice to mount a subsequent proliferative response to LACK and further delayed the onset of lesion development in infected mice. However, pretreatment with CTB-LACK did not prevent the eventual onset and progression of disease in these mice. An examination of cytokine responsiveness to LACK after tolerization with CTB-LACK revealed that while the Th1 response to LACK was suppressed, Th2 cytokine production was unaffected. Similar experiments using an ovalbumin-CTB conjugate suggested that this selective tolerance of Th1 cells was not specific to the LACK protein but may be an effect common to CTB-conjugated proteins.