The potential pathogenetic link between peripheral immune activation and the central innate immune response in neuropsychiatric systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology. Neuropsychiatric disturbances unexplained by drugs or by other untoward manifestations of disease are present in up to one-half of SLE patients and have profound economic and social impact. In patients with neuropsychiatric SLE, structural lesions have been identified in the hippocampus and proinflammatory cytokines have been detected in the cerebrospinal fluid. Similarly, murine models of lupus, such as MRL-lpr/lpr mice display behavioral disturbances which map to the hippocampus and exhibit overexpression of proinflammatory cytokine genes in hippocampal homogenates. Neuropsychiatric SLE typically occurs in the presence of serologically and clinically active lupus. In animal models of SLE, such as MRL-lpr/lpr, NZB, BXSB, and [NZB x NZW]F(1), uncontrolled autoreactivity in the periphery is accompanied by behavioral disturbances that are chronic and progressive. These observations suggest the hypothesis that central nervous system disease in SLE is driven by cross-talk between the peripheral immune system and the brain's innate immune system, which results in the inexorable activation of astrocytes, microglia, and/or neurons within the hippocampus. This leads to overproduction of brain cytokines, which induce the synthesis of pro-oxidant molecules, such as eicosanoids and reactive oxygen species, with resultant tissue injury. The cascade becomes self-perpetuating and eventuates in neuronal death, which is followed by impaired cognition. A better understanding of the molecular events that operate in the pathogenesis of neuropsychiatric SLE may provide the basis for a more rational therapeutic approach to this incompletely understood disease.