Comparison of serum and cell-specific cytokines in humans.

Cytokines function at the cellular, microenvironmental level, but human cytokine assessment is most commonly done at the macro level, by measuring serum cytokines. The relationships between serum and cellular cytokines, if there are any, are undefined. In a study of hospitalized patients in Malawi, we compared cytometrically assessed, cell-specific cytokine data to serum interleukin 2 (IL-2), IL-4, IL-6, IL-8, IL-10, gamma interferon (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha) levels in 16 children and 71 (IL-2, -4, -6, -10) or 159 (IL-8, IFN-gamma, and TNF-alpha) adults, using Wilcoxon rank sum tests and Pearson's (r(p)) and Spearman's (r(s)) rank correlations. For the entire study group, correlations between identical serum and cellular cytokines mainly involved IL-8 and IFN-gamma, were few, and were weakly positive (r < 0.40). Blood culture-positive persons had the most and strongest correlations, including those between serum IL-2 levels and the percentages of lymphocytes spontaneously making IL-2 (r(s) = +0.74), serum IL-8 levels and the percentages of lymphocytes spontaneously making IL-8 (r(p) = +0.66), and serum IL-10 levels and the percentages of CD8(+) T cells making TNF-alpha (r(p) = +0.89). Human immunodeficiency virus (HIV)-positive persons had the next largest number of correlations, including several serum IL-8 level correlations, correlation of serum IL-10 levels with the percentages of lymphocytes producing induced IL-10 (r(s) = +0.36), and correlation of serum IFN-gamma levels and the percentages of lymphocytes spontaneously making both IL-6 and IFN-gamma in the same cell (r(p) = +0.59). HIV-negative, malaria smear-positive, and pediatric patients had few significant correlations; for the second and third of these subgroups, serum IL-8 level was correlated with the percentage of CD8(-) T cells producing induced IL-8 (r(s) = +0.40 and r(s) = +0.56, respectively). Thus, the strength of associations between serum and cellular cytokines varied with the presence or absence of bloodstream infection, HIV status, and perhaps other factors we did not assess. These results strongly suggest that serum cytokines at best only weakly reflect peripheral blood cell cytokine production and balances.

Cytokines and malaria parasitemia.

The balance between pro- and antiinflammatory cytokines may be important in malaria presentation and outcome. Malaria tends to be more severe in children than in adults, presumably because partial immunity develops with age. However, the full nature of, and age-related differences in, anti-malarial immunity are unknown. We compared: (1) serum and cell-specific cytokines of patients with acute malaria to those of patients with other acute illnesses and to those of healthy adults and (2) the cytokine responses of parasitemic children and parasitemic adults. Flow cytometry was done on the peripheral blood mononuclear cells of 148 hospitalized children, 161 febrile hospitalized adults, and 20 healthy adults in Malawi, Africa, a malaria-endemic country. Serum cytokines were also assessed for 80 of these patients. Thirty-eight participants were parasitemic with Plasmodium falciparum. Serum interleukin (IL)-10 (an antiinflammatory, immunoregulatory, and type 2 cytokine) levels were higher in malaria patients than in other patients (medians 502 pg/mL vs 16 pg/mL, P = 0.002), and the percentages of various lymphocyte populations making IL-6 (a proinflammatory, type 2 cytokine regulating iron distribution) were lower in malaria patients than in other patients (e.g., for spontaneous production by children's CD8(+) T cells: medians 1.4% vs 33.1%, P = 0.004). For adult patients, the percentages of lymphocytes spontaneously making IL-4 (a type 2 cytokine) were significantly lower in those with malaria than in those without malaria (medians 0.9% vs 2.1%, P = 0.005). The percentages of monocytes spontaneously making IL-8 (a chemotactic, proinflammatory chemokine) were higher in parasitemic children than in parasitemic adults (medians 5.8% vs 1.7%, P = 0.003). A number of cellular proinflammatory, type 1 parameters were significantly higher in all children (with or without malaria) than in all adults; these included the percentages of various lymphocyte populations making IL-6, both IL-6 and interferon-gamma, or IL-8. These data support the importance of IL-10 in malaria parasitemia. Given the lack of an IL-4 (type 2) response, IL-10's primary role may be immunoregulatory rather than type 2 in nature. In this study, the immune response to malaria was more proinflammatory in children than in adults. This difference, if corroborated by other studies, could be related to malaria's greater severity in children.

Immune determinants of organism and outcome in febrile hospitalized Thai patients with bloodstream infections.

Opportunistic infections (OI) and the human immunodeficiency virus (HIV) cause significant morbidity and mortality in developing countries. Immune cell and cytokine profiles may be related to the type and course of OI and to the OI-HIV interaction. Examining cell-specific cytokine production ex vivo has only recently become feasible. In Thailand, 53 febrile, hospitalized adults were enrolled in a study of the immune correlates of bloodstream infections (BSI). On site, blood cells were stimulated ex vivo. Cell-surface antigens and eight intracellular cytokines were subsequently analyzed using flow cytometry to determine associations with mortality and the organism causing the BSI. By logistic regression analysis, the percentage of CD3(+) CD16/56(+) cells making tumor necrosis factor alpha (TNF-alpha) (P = 0.033) and the percentage of CD3(-) CD16/56(+) cells (NK) (P = 0.032) were related to HIV positivity. Lymph node enlargement with HIV infection and the percentage of CD3(+) CD16/56(+) making TNF-alpha were predictive of death. A lower percentage of CD3(+) CD8(+) lymphocytes making interleukin-8 (IL-8) (P = 0.005), fewer monocytes expressing CD14 (P = 0.009), and the percentage of CD3(+) CD8(+) cells producing gamma interferon (P = 0. 011) were associated with blood culture positivity and the causative organism. For every one point decrease in the percentage of CD3(+) CD8(+) cells making IL-8, the likelihood of a positive culture increased 23%; for every one point decrease in the percentage of monocytes expressing CD14, the likelihood of a positive culture increased by 5%. Only a few immune cell types and three of their related cytokines were significantly associated with HIV disease outcome or the BSI organism. These cell types did not include CD3(+) CD8(-) cells (a surrogate for CD4(+) cells), nor did they involve cytokines associated with a type I to type II cytokine shift, which might occur with advancing HIV infection. These associations support the premise that CD8(+) and CD16/56(+) lymphocytes play significant roles in HIV and type I infections.