Longitudinal analysis of pro- and anti-inflammatory cytokine production in severely fatigued adolescents
Introduction
Fatigue is a widespread phenomenon among adolescents and is often attributed to pubertal hormonal, psychological, educational, and social changes. Epidemiological data from an adolescent population recently demonstrated that fatigue was strongly related to pain, unrefreshing sleep and cognitive problems (Ter Wolbeek et al., 2006). In addition, fatigued participants reported higher levels of depressive symptoms and anxiety. Girls were more affected with fatigue than boys (3:1 gender ratio). About 16% of the female population suffered from severe fatigue for one month and 10% reported fatigue duration of more than three months, resulting in high rates of school absenteeism (Ter Wolbeek et al., 2006). Findings in adults suggest that unexplained severe fatigue is a predictor for later development of chronic fatigue syndrome (CFS) (Wessely et al., 1995, Huibers et al., 2004). Therefore, followup studies concerning symptoms and underlying mechanisms of fatigue in adolescents are of utmost importance in the scope of prevention of the development of CFS later in life.
According to the Centers for Disease Control and Prevention (CDC) definition, CFS is characterized by persistent and debilitating fatigue for at least six months, accompanied by complaints such as headaches, myalgia, joint pain, unrefreshing sleep, and memory and concentration disturbances, which are not explained by somatic or psychiatric illness (Fukuda et al., 1994). Symptoms of depression and anxiety are also often observed in patients with CFS (Roy-Byrne et al., 2002, Garralda and Rangel, 2005, van de Putte et al., 2006). This cluster of symptoms resembles the non-specific symptom constellation that occurs during an immune response to pathogens or cytokine administration, also called “sickness behavior” (Dantzer, 2001). Although fatigue duration in our previous study was monitored shorter than six months, the participants showed many similarities in symptomatology with sickness behavior and with CFS patients (Ter Wolbeek et al., 2006).
The suggested involvement of viral infections (i.e. Lyme disease, Q fever, infectious mononucleosis) in the development or precipitation of chronic fatigue, and the similarities between CFS and sickness behavior symptomatology resulted in numerous studies focusing on immune functions in CFS patients. Increased production of pro-inflammatory cytokines secreted either by monocytes or T-cells, including interleukin (IL)-1, IL-6, tumor necrosis factor (TNF)-α and interferon (IFN)-γ, may account for sickness behavior-like symptoms, in which fatigue has a central role (Dantzer, 2001). Gaab et al. (2005) observed positive relations between fatigue and in vitro production of pro-inflammatory monocyte TNF-α in adult CFS patients and between fatigue and IL-6 in both adult CFS patients and healthy participants. However, other studies suggested an anti-inflammatory polarity with relatively high levels of IL-4 and IL-10 in CFS patients (Skowera et al., 2004). Visser et al., 1998, Visser et al., 2001 reported higher levels of monocyte IL-10 and a reduction in IFN-γ production by purified CD4+ T-cells in adult CFS patients. In contrast to these reports in adults, little is known about immune function in adolescents. One study reported higher mitogen-induced T-cell proliferation, but no differences in monocyte production of TNF-α and IL-10 between CFS patients and controls (Kavelaars et al., 2000). Overall, results on immune functions of CFS patients are present but often contradictory (Patarca, 2001, Lyall et al., 2003, Cho et al., 2006). In a review by Natelson et al. (2002) about the question whether CFS is associated with a stable immune dysfunction, the authors had to conclude that it is still absolutely unclear whether immunological dysfunctions play a role in the symptom complex of CFS. Whatever the immunological outcome of previous studies in CFS patients, the resemblance of symptoms of severely fatigued adolescents from our epidemiological study and CFS patients raised the question whether and to what extent alterations in immune function would be present in severely fatigued adolescents.
The majority of studies analyzing immune functions in CFS have the limitation that these studies rely on single point measurements without considering the influence of factors such as seasonal variation in immune reactivity, diurnal variation and exposure to common infections (van Rood et al., 1991, Nelson, 2004). This may partly explain the inconsistency between the results of these studies. When studying subtle differences between groups, between-subject variability due to these confounders should be minimized. Segerstrom et al. (2006) argued, based on a simian study, that even up to ten assessments of the same animal are required to determine an average immune status or “immune trait”.
Thus, the aim of the present study was to identify immune deviations in severely fatigued adolescents as compared to non-fatigued individuals. To reliably assess immunological parameters and to explore the within-subject stability of immune measures in humans, we chose a longitudinal design. In a sample of non-fatigued and severely fatigued adolescents we examined T-cell proliferation and pro- and anti-inflammatory cytokine production in vitro on three different time points: T1 (spring), T2 after six months (autumn) and T3 after 12 months (spring). In addition, identical immunological parameters were analyzed in a small group of adolescent CFS patients in order to identify possible proportional alterations in immune function. Since the prevalence of severe fatigue in our epidemiological study was higher in girls and female predominance was also found in some other studies about fatigue and CFS during adolescence (Wright and Beverley, 1998, Farmer et al., 2004, Ter Wolbeek et al., 2006), only female adolescents were included in the present study.
Section snippets
Participants
Non-fatigued and severely fatigued participants were selected from a broader epidemiological study on fatigue among adolescents at five Dutch high schools (Ter Wolbeek et al., 2006). All female participants and their parents (or guardians) received written information about the current study. Required sample size was determined by power analysis. Using at least 55 children in each group and with a standard deviation of 205 (Kavelaars et al., 2000) on one of the most important immune parameters,
Demographics
A total of 67 severely fatigued girls and 61 non-fatigued girls as well as 11 CFS patients were included in the study. In Table 1 the demographic characteristics of the participants are summarized. Between fatigued and non-fatigued girls, no differences were observed in age, BMI, medication use, use of oral contraceptives and self-reported allergies. Fatigued girls were in more advanced stages of pubertal development (Tanner, pubic hair) (χ2 = 7.88, p < .05) and a higher proportion of this group
Discussion
In the present paper we examined whether severely fatigued female adolescents, who have symptom similarities with CFS patients and with the symptom constellation of sickness behavior, would show immunological changes in the level of mitogen-induced T-cell proliferation and T-cell mitogen- or LPS-induced pro- and anti-inflammatory cytokine production compared to non-fatigued participants. During all three time points across the year of the study severely fatigued participants reported higher
Acknowledgments
We thank Mrs. M. Maas, Mrs. M.M. Ringeling, Mrs. E. Luijk, Mrs. C.D.J. Tersteeg-Kamperman, and Mrs. J. Zijlstra for their contribution to the data collection and for performing all laboratory analyses.
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