Humoral immune response to natural infection with Encephalitozoon cuniculi in rabbits.

Sera from 4 generations of a family of rabbits having a natural Encephalitozoon cuniculi infection were investigated. Antibodies were demonstrated in a litter of newborn rabbits and in another litter 11 days old. Histoloigcal examination of the brains and kidneys of these animals failed to reveal lesions attributable to the disease. Sera from a further litter of 2 rabbits, taken at weekly intervals from 4 to 42 weeks of age, revealed a low initial antibody titre which regressed to an undetectable level. After an interval, titres rose and then plateaued to the end of the period of observation. Encephalitozoon cuniculi infections in the dams of all the litters were confirmed by antibody assay and by histology. Parallel titration of samples treated and not treated with 2-mercaptoethanol showed that the india-ink immunoreaction demonstrates only immunoglobulin G.