Natural killer (NK) cells are the primary immune cell that targets and removes measles-infected cells. Therefore, any weakness in this defense would lead to a more severe outcome. In this study of 30 individuals with acute measles, the ability of their NK cells to lyse (kill) measles-infected cells was approximately half that found in other infections. This highlights the importance of identifying interventions to enhance both the quantity and quality of NK cells. Notably, the cytokine interferon-2, also known as IL-2 (essential for NK function), was low or undetectable in all measles patients. As IL-2 was shown to partially restore NK activity, this suggests further investigation is warranted, as it could potentially be of value in reducing illness severity.
ABSTRACT
Natural killer cells are postulated to play an important role in host anti-viral defences. We measured natural killer cell activity in 30 individuals with acute measles (73 +/- 21 lytic units (LU)/10(7) cells) and 16 individuals with other infectious diseases (149 +/- 95 LU) and found it reduced compared with values for adults (375 +/- 70 LU; P less than 0.001) or children (300 +/- 73 LU, P less than 0.01) without infection. Reduced natural killer cell activity was found in measles patients with (84 +/- 30 LU) and without (55 +/- 18 LU) complications and was present for at least 3 weeks after the onset of the rash. Activity was increased by in vitro exposure of cells to interleukin-2. Depressed natural killer cell activity parallels in time the suppression of other parameters of cell-mediated immunity that occurs during measles.