Ratio of M2 macrophage expression is closely associated with poor prognosis for Angioimmunoblastic T‐cell lymphoma (AITL)

Angioimmunoblastic T-cell lymphoma (AITL) is a peripheral T-cell lymphoma characterized by systemic disease with polymorphous infiltrate including macrophages. Although many studies of tumor-associated macrophage (TAM) populations in various malignant tumors have been published, only a few have dealt with activation of macrophage phenotypes such as M1 and M2 in tumor tissue. Because M2 macrophages highly express CD163, we suspected that CD163 may be a useful marker for identification of activation of macrophage phenotypes in AITL. We performed a retrospective study of immunohistochemical expression using two markers for macrophages [CD68 (PG-M1), CD163] and of the correlation of these expressions with overall survival of 42 AITL patients. The number of CD68-positive cells in AITL tissues did not correlate with overall survival (P= 0.59), whereas the number of CD163-positive cells and overall survival correlated to some extent (P= 0.08). Meanwhile, a higher ratio of CD163-positive to CD68-positive cells in AITL significantly correlated with worse overall survival (P= 0.036). Considering that this ratio reflects the proportion of macrophages polarized to the M2 phenotype, our findings indicate that activation of macrophages towards the M2 phenotype correlates with worse prognosis. Our findings indicate that the ratio of M2 macrophages expressed may be a useful marker for prognosis of AITL.