Although its frequency in nations with excellent obstetric services has fallen below 1/500 pregnancies, it is still common in many other countries. The primary pathology is in the placenta, which secretes an anti-angiogenic factor in response to ischaemia, leading to endothelial dysfunction. In fatal cases, there are arterial lesions in many organs including the brain. This is the second most frequent organic psychosis, and the second to be described. Psychoses occur in about 5% of cases, and about 240 detailed cases have been reported. It particularly affects first time mothers. Seizures may begin before, during or after labour, but the onset of psychosis is almost always postpartum. These mothers usually experience delirium but some have manic features. The duration is remarkably short, with a median duration of 8 days. This, together with the absence of a family history and of recurrences, contrasts with puerperal bipolar/cycloid psychoses. After recovery, amnesia and sometimes retrograde memory loss may occur, as well as other permanent cerebral lesions such as dysphasia, hemiplegia or blindness. A variant was described by Donkin . He had been trained by Simpson (one of those who first recognized the importance of albuminuria) in Edinburgh, and recognized that some cases of eclamptic psychosis occurred without seizures; this explains the interval between seizures (or coma) and psychosis, a gap that has occasionally exceeded 4 days: seizures and psychosis are two different consequences of severe gestosis.
T cell activation is tightly controlled and generally requires a very strong MHC/antigen activation signal, or additional activation signals provided by "helper" T cells (see below). Helper T cells
Helper T cells regulate both the innate and adaptive immune responses and help determine which immune responses the body makes to a particular pathogen. These cells have no cytotoxic activity and do not kill infected cells or clear pathogens directly. They instead control the immune response by directing other cells to perform these tasks.Helper T cells express T cell receptors that recognize antigen bound to Class II MHC molecules. The MHC:antigen complex is also recognized by the helper cells CD4 co-receptor, which recruits molecules inside the T cell (such as Lck) that are responsible for the T cells activation. Helper T cells have a weaker association with the MHC:antigen complex than observed for killer T cells, meaning many receptors (around 200–300) on the helper T cell must be bound by an MHC:antigen to activate the helper cell, while killer T cells can be activated by engagement of a single MHC:antigen molecule. Helper T cell activation also requires longer duration of engagement with an antigen-presenting cell. The activation of a resting helper T cell causes it to release cytokines that influence the activity of many cell types. Cytokine signals produced by helper T cells enhance the microbicidal function of macrophages and the activity of killer T cells.