Early major histocompatibility complex (MHC) class I antigen induction in hypothalamic supraoptic and paraventricular nuclei in trypanosome-infected rats

Sprague-Dawley rats were injected intraperitoneally with a suspension of Trypanosoma brucei. An early induction of major histocompatibility complex (MHC) class I antigens as well as an infiltration of macrophage-like and cytotoxic T-cells was detected with immunohistochemical techniques in circumventricular organs, such as the median eminence, neurohypophosis, subformical organ, pineal gland and area postrema. These areas, which lack a blood-brain barrier, correspond to those showing early invasion of trypanosomes. In addition, there was a marked induction of MHC class I in neurons in two hypothalamic nuclei, The paraventricular and supraoptic nuclei. Neurons in these two nuclei are located behind the blood-brain, but project to the neurohypophysis and to the medain eminence, thereby exposing their axon terminals to factors circulating in the blod or released locally from invading trypanosomes or from macrophages or cytotoxic T-cells. It is suggested that the alteration in the nerve cell bodies in the hypothalamic nuclei is caused by retrograde axonal signals from these target areas. Sleeping sickness; Trypanosomes; Paraventricular nucleus; Major histocompatibility complex classI