Monoclonal antibodies against leishmanial membranes react with specific excreted factors (EF)

The interaction was examined between two reagents used for the speciation of Leishmania: spent culture-medium excreted factors (EF) and antileishmanial monoclonal antibodies (MCA). Thirty-three MCAs: seven against L. major, five against L. tropica, eight against L. aethiopica, 11 against L. donovani sensu lato and two against all Leishmania species were screened by double diffusion for reactions with EFs representing seven different sub-serotypes (A₁, A₂, A₄, B₁, B₂, B₃ and A₃,B₂). Only five MCAs showed any reactivity. Three MCAs to L. major (T1, T2 and T7) precipitated only sub-serotype A₁ en A₄ EF, and two MCAs to L. tropica (T11 and T15) precipitated only sub-serotype A₂ EF. Leishmania major and L. tropica are both serotype A species. None of the antiL. aethiopica and antiL. donovan MCAs reacted with any of the EF preparations. Both of these species belong to the serotype B. MCAs T11 and T15, the first recorded with a specificity for only sub-serotype A₂ EF, were tested further against 28 sub-serotype A₂ and three sub-serotype A₂B₂ EFs from L. tropica strains. All 31 EFs formed visible bands with standard rabbit polyclonal antileishmanial serotype A serum. Only 18 of them precipitated with T11 and T15, even though parasite lysates prepared from promastigotes of several non-reactors tested positive with the MCAs. The lack of homogenous reactivity with T11 and T15 among the A₂ EFs suggests that the EFs from these strains possess structural differences which affect EF-MCA precipitation.