MHC Class II proteins are limited to immune cells expressly antigen presenting cells like macrophages, B cells, dendritic cell of the spleen, Langerhans cell of the skin, active CD4+ T cell - MHC Class III proteins are soluble antigens which are secreted in circulation and stay zero cost in plasma. Some of the traits that we have are based on simple inheritance where one version of a gene (dominant allele) masks the expression of the other version of that gene (recessive allele). In PHP, parathyroid hormone is generate in normal amounts by the parathyroid gland and emancipate into the blood.