CRISTINA GRIGORESCU, LIVIU CIPRIAN GAVRIL, LAURA GAVRIL, TIBERIU LUNGULEAC, BOGDAN MIHNEA CIUNTU, DELIA HINGANU, ALEXANDRU PATRASCU, PAUL SALAHORU USE OF IMMUNOHISTOCHEMISTRY TO ESTABLISH ETHIOLOGY IN THE CASE OF PRIMARY SPONTANEOUS PNEUMOTORAX PATIENTS Primary spontaneous pneumothorax has a complex morphopathological substrate, in which active smoking plays an essential etiopathogenic role. Inflammation of the distal airways, bronchial anomalies, perivascular eosinophilic infiltrate associated with hereditary factors and physiognomy (longilli patients) lead to obstruction of distal airwayswhich is the essential element in the emergence of emphysematous changes. Immunohistochemistry (IHC) is a technique used to identify cellular or tissue (antigens) constituents by Ag-Ac, the Ac link site being identified either by direct labeling of the antibody or by a secondary labeling method. IHC reactions are based on tissue-antibody antigen binding, the latter being evidenced by direct conjugation to tracer molecules (direct reaction) or by another chain of other labeled free antibody linkages. We can consider the immunohistochemical method as having a potential utility, especially in selected patients, where there are sufficient clinical and epidemiological reasons to suspect a pneumothorax-causing disease but where the classical investigations did not provide diagnostic performance.