Immune System and Neurotrophic Factors in Autism

Evidences related to the fact that there is a immunological functional disorder in autism are gradually increasing. Since immunological mechanisms play a role in the neuronal cell migration, axonal development and formation of synapses, it is mentioned that there is an immune mediated inflammatory period exists (Bradstreet et al. 2007). Central nervous system and immune system are systems which are in interaction with each other and which are complex and highly developed (Ashwood and Water 2004). Immune cells and molecules play an important role in forming the brain functions by affecting the cognitive and emotional processes. These molecules have various effects such as infection, inflammation and injury on neural tissues, the modulation of central nervous system response and systematic response. It is indicated that proinflammatory cytokines such as interleukin (IL) – 1, IL -6, IL – 12, interferon (IFN) gamma and tumor necrosis factor (TNF)alpha in particular directly affect the neural function and development by playing a role in the neurodevelopmental process. Applying the cytokines such as IFN – alpha, IL – 2, TNF– alpha at therapeutical doses lead to the symptoms such as depression, sleep disorder, defects in cognitive functions, motivational change and decline in behavior of making research. It is reported that cytokines applied systematically may lead to increase in hypothalamus, hippocampus and nucleus accumbance and in noradrenergic, dopaminergic and serotenergic metabolism, and it may change the synaptic plasticity and therefore may affect the memory and learning processes (Ashwood et al. 2006). Findings which states that response of maternal immune to the infection, affect the fetal brain development through the increase in the cytokine level on circulation and which are collected from animal models support the role of immune system in the etiology of autism (Yamashita et al. 2003, Patterson 2002). It is mentioned that there is “abnormal” immune findings exists in 15 – 60 % of the autistic children (Pardo et al 2005). Two basic immune fuctional disorders in autism are associated with immune formation that includes autoimmunity and proinflammatory cytokines. The decline in the number of the CD4 lymphocyte numbers, the change of balance of T helper cell type 1(Th1)/ T helper cell type 2 (Th2) in the direction of Th2 and the response corruption of Th1 (corruption in cell mediated immunity), the decline in the T lymphocyte response against mitogens, the decline in the natural killer’s functions and corruption shown by declined IgA level in humoral immunity are among immune system abnormalities indicated in autism (Cohly and Panja 2005, Careaga et al. 2010).