Major histocompatibility complex class II (MHC II) expression in the normal and pathological human foetal spinal cord.

The ability of the specific immune response of organisms is determined by the possibility of synthesis, transport and presentation of the major histocompatibility complex class II (MHC II) molecules on the surface of antigen-presenting cells. MHC II molecules are responsible for the binding, transport and presentation of a foreign antigen to helper T lymphocytes. They also stimulate the multiplication of specific B lymphocytes and determine the type of antibodies produced. The expression of MHC II molecules on the cellular surface of the spinal cord in cervical, thoracic, lumbar and sacral regions was studied on 30 normal human foetuses between 11 and 22 weeks of gestation (GW) and 9 foetuses with genetic defects (Down syndrome, mucopolysaccharidosis, mucoviscidosis or Nori's syndrome) between 17 and 22 GW. The immunocytochemical presence of MHC II molecules was found in all regions of the spinal cord in both groups of foetuses, normal and pathological, during the whole interval under study. The molecules were dispersed in the grey and white matter of the spinal cord and located most frequently on the surface of cells, near the central canal and blood vessels. These cells corresponded morphologically and immunocytochemically with amoeboid and ramified microglia. No differences in MHC II expression between the spinal cord regions or between normal foetuses and those with genetic defects were noted. It seems likely that such an early occurrence of MHC II expression in the spinal cord of foetuses with normal development, as well as the absence of abnormalities in this expression in foetuses with genetic defects, may indicate the significant role of these molecules in the immunological protection of the foetus and thus ensuring normal embryogenesis.