Recently, CD32, a low-affinity receptor for the IgG Fc fragment with no previously reported expression on T cells, has been described as specific surface marker of latently HIV infected CD4+ T cells. As most of the current findings are based on in vitro experiments and little is known about the frequency and distribution, we studied the CD32 expression on CD4+ T cell naïve and memory populations in blood and lymph nodes of HIV patients and healthy individuals.
We analyzed peripheral blood samples of 36 HIV-1 infected patients (n=23 viremics/13=ART treated) and healthy individuals (n=14) using a multi-parametric flow cytometry determining surface expression of CD3, CD8, CD4, CD45RA, CCR7, CD27, CD25, CD127, CCR5, CCR6, CXCR4. Additionally, cells from 8 lymph nodes of HIV patients and uninfected individuals were examined.
Overall, expression of CD32 differed only slightly on total peripheral CD4+ T cells between viremic HIV patients, ART-treated and healthy individuals. The highest expression was found in peripheral memory CD4+ T cell sub populations of viremic patients. CD32+ CD4+ T cells showed higher immune activation and higher expression of CCR5+. Furthermore, expression of CD32 on total CD4+ T cells and memory T cell populations of viremic patients correlated with general cellular immune activation and integrated viral DNA. Compared to blood, CD32 expression was generally lower in lymph nodal CD4+ T cells.
In line with previous reports on the nature of reservoir cells, effector memory cells expressed CD32 with a higher frequency. However, we hypothesize that the relationship between CD32 and the reservoirs of latently infected T cells is more complex as other host factors and immune activation seem to influence CD32 expression. Follow-up studies will have to re-evaluate CD32 as definite marker of latently HIV-infected CD4+ T cells.