CD45 immunoaffinity depletion of vesicles from Jurkat T cells demonstrates that exosomes contain CD45: no evidence for a distinct exosome/HIV-I budding pathway

The presence of relatively high levels of cellular protein contamination in density-purified virion preparations is a confounding factor in biochemical analyses of HIV and SIV produced from hematopoietic cells. A major source of this contamination is from vesicles, either microvesicles or exosomes, that have similar physical properties as virions. Thus, these particles can not be removed by size or density fractionation. Although virions and vesicles have similar cellular protein compositions, CD45 is excluded from HIV-I yet is present in vesicles produced from hematopoietic cells. By exploiting this finding, we have developed a CD45 immunoaffinity depletion procedure that removes vesicles from HIV-I preparations. While this approach has been successfully applied to virion preparations from several different cell types, some groups have concluded that "exosomes" from certain T cell lines, specifically Jurkat, do not contain CD45. If this interpretation is correct, then these vesicles could not be removed by CD45 immunoaffinity depletion. Here we show that dense vesicles produced by Jurkat and SupTI/CCR5 cells contain CD45 and are efficiently removed from preparations by CD45-immunoaffinity depletion. Also, contaminating cellular proteins were removed from virion preparations produced by these lines. Previously, the absence of CD45 from both "exosomes" and virions has been used to support the so called Trojan exosome hypothesis, namely that HIV-I is simply an exosome containing viral material. The presence of CD45 on vesicles, including exosomes, and its absence on virions argues against a specialized budding pathway that is shared by both exosomes and HIV-I.

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