Mechanism of innate immunity and inheritance of resistance to Cryptobia salmositica in Salvelinus fontinalis

One hundred of 203 laboratory raised brook charr (Salvelinus fontinalis) were resistant to Cryptobia salmositica infection. Susceptibility was not related to age nor to route of infection. Plasma of resistant charr lysed the parasite. However lytic effects of plasma of resistant charr were lost after heat-inactivation or after treatment with ethylenediaminetetraacetic acid (EDTA). Addition of Mg{dollar}sp{lcub}2+{rcub}{dollar} ions to EDTA chelated plasma of resistant charr restored lytic effects. Treatment with ethylenebis-(oxyethylenenitrila)tetraacetic acid, a Ca{dollar}sp{lcub}2+{rcub}{dollar} chelating agent, or cobra venom factor did not reduce lytic effects of plasma from resistant charr. The alternate pathway of complement activation is the mechanism of innate resistance. Four resistant and four susceptible male charr were crossed with two susceptible females. Susceptibility of the progenies was determined four weeks post-inoculation of the parasite. The results suggest a single Mendelian locus determines resistance to C. salmositica infection in brook charr.