77. Mechanical processing of tissue suppresses NK cytotoxicity of resident leukocytes through the release of humoral factors

Abstract

We previously reported that marginating-pulmonary (MP) cells, leukocytes which reside within and adhere to the lung capillaries, are unique in persistently containing activated NK cells and in exhibiting high lysis capacity against various autologous “NK-resistant” target cells. Here we attempted to delineate the relative significance of MP-NK cells within the entire lung NK cytotoxic ability. Thus, we compared the cytotoxicity of MP-NK cells, collected by forced lungs perfusion, to cytotoxicity of the entire lung cell population following mechanical mincing of the lungs tissue. Whereas MP-leukocytes exhibited profound cytotoxicity (50–80%), the entire lungs cell population displayed minimal levels (up to 20%), although containing equivalent number of NK cells (CD161++), suggesting that some processes induced by lung mincing suppress NK cytotoxicity. Indeed, washing of this preparation, or Ficoll-Paque-based enrichment and washing, increased lysis capacity, but only slightly. Moreover, co-incubating MP-NK cells with supernatant harvested from minced lungs tissue markedly reduced MP-NK cytotoxicity in a dose and time dependent manner, and the supernatant contained significant levels of IL-10, IL-6, and IL-1-beta. These compounds, as well as TGF-beta and PGE2, suppressed MP-NK cytotoxicity in vitro. Similar findings were observed following mincing of liver tissue. Overall, these findings indicate that the procedure of tissue mincing entails a release of certain NK-suppressing factors, which are currently targeted in our on-going studies, factors that may distort ex-vivo findings from processed tissue.