*3.4.3. Serologic markers*

Beta-2 microglobulin is a low molecular weight protein, which comprises the light chain of class 1 MHC proteins and is noncovalently bound to the heavy chain [2]. It is present on the surface of all nucleated cells. Dissociation during metabolism and degradation leads to its release to all biological fluids. In HIV disease, an increased level of Beta-2 microglobulin in cerebrospinal fluid (CSF) correlates with the disease progression and a decrease level indicates successful therapy [32].

Similarly, neopterin, a marker of immune activation is a low molecular weight compound derived from guanosine triphosphate [5]. It is produced by monocyte/macrophages upon stimulation with IFN-γ. The production is increased in HIV infection and infection by intracellular organisms such as parasite, autoimmune disease, malignant tumours, allograft rejection, neurological as well as cardiovascular disease [33]. However, it has slightly low predictive value compared to beta-2 microglobulin [5]. Neopterin and beta-2 microglobulin levels were proved to be significant predictors of AIDS risk in HIV-1 seropositive patients. The predictive value of both parameters is equal to CD4+ T cell counts. Therefore, neopterin and beta-2 microglobulin are recommended to be used as an additional marker to predict AIDS risk for HIV-1 seropositive patients and is beneficial particularly in the setting where the CD4+ T cell count measurement is not available [34].
