key: cord-0001195-gyetna96 authors: Wong, Samuel Yeung Shan; Wong, Chun Kwok; Chan, Frank Wan Kin; Chan, Paul K. S.; Ngai, Karry; Mercer, Stewart; Woo, Jean title: Chronic psychosocial stress: does it modulate immunity to the influenza vaccine in Hong Kong Chinese elderly caregivers? date: 2012-07-08 journal: AGE DOI: 10.1007/s11357-012-9449-z sha: 53114f0f5e6fdc237988a366cd9af65372e959c9 doc_id: 1195 cord_uid: gyetna96 Previous studies evaluated the effects of psychosocial stress on influenza vaccine responses. However, there were methodological limitations. This study aims to determine whether chronic stress is associated with poorer influenza-specific immune responses to influenza vaccines in Hong Kong Chinese elderly people. This is a prospective study with a 12-week follow-up. Subjects were recruited from government general out-patient clinics, non-government organizations, and public housing estates in Hong Kong. Participants include 55 caregivers of spouses with chronic conditions that impaired their activities of daily living and 61 age- and sex-matched non-caregivers. A single-dose trivalent influenza vaccine was given to all subjects by intramuscular ingestion. Blood samples were collected before vaccination, at 6 weeks, and at 12 weeks after vaccination. Influenza vaccine strain-specific antibody titers were measured by the hemagglutination inhibition method. Lymphocyte subsets were analyzed for ratios and absolute counts, and cytokine concentration were measured by flow cytometry. Validated scales were used to assess psychological (depressive symptoms, perceived stress, and caregiver strain), social (multidimensional social support scale), and lifestyle factors (physical exercise, cigarette smoking, and alcohol consumption) at baseline prior to vaccination. Demographic and socioeconomic variables were also collected. Albumin levels were measured as an indicator for nutritional status in subjects. Caregivers had statistically significant (p < 0.05) lower cell-mediated immune responses to influenza vaccination at 12 weeks when compared with those of the controls. No differences in humoral immune response to vaccination were observed between caregivers and controls. Hong Kong Chinese elderly who experience chronic stress have a significantly lower cell-mediated immune response to influenza vaccination when compared with non-caregivers. It has been shown that psychological stress can reduce immune responses (Graham et al. 1986; Glaser et al. 1987; Cohen et al. 1991 Cohen et al. , 1993 Cobb and Steptoe 1996; Cohen et al. 1998; Ginaldi et al. 2001) and that there are multiple communications between and among the nervous, endocrine, and immune systems (Glaser et al. 1999) . This relationship between stress and immunity is particularly significant in the older population (Ginaldi et al. 2001 ) because of an age-related reduction in bodily immune functions. In respiratory infections, influenza viruses are among the most studied because of their significant impact on morbidity and mortality in the older population (Hoyert et al. 1999; Yap et al. 2004) . As life-expectancy increases around the world, many elderly people become the main caregivers to their spouses and/or their parents (Braithwaite 1996) . Studies in western countries on elderly caregivers with high levels of stress have found prolonged endocrine and immune dysregulation, including alterations in vaccine response (Gravenstein et al. 1994; Kiecolt-Glaser et al. 1996) . Older adults with poorer responses to vaccines also have higher rates of clinical illness including influenza virus infections (Gravenstein et al. 1994) . As influenza vaccine efficacy is much lower in the elderly when compared with young adults (Berstein et al. 1999) , chronic stress could further decrease the vaccine efficacy in this population which could be of public health significance. With emerging viral infections such as SARS and "avian flu," and the aging of post-war baby boomers (in a Western context), research aimed at understanding the various influences on the health and immune functions of older adults is of considerable public health importance. Although studies have been conducted in majority Caucasian populations in temperate regions, no studies have been conducted to evaluate the impact of chronic stress on modulating the immune responses to influenza vaccination in an Asian population or in the tropics. Culture-or race-specific studies are important because stress experiences may differ among different cultures, and it has been shown that racial and cultural factors are important determinants of stress experience (Connell and Gibson 1997; Valentine et al. 1998) . For example, members of collectivistic cultures that exist in Asia are associated with less caregiver strain (Garnaccia and Parra 1996) and receive better social support from their family networks (Ell 1996; Ohaeri 1998; McCabe et al. 2003) . Besides possible cultural influences on the caregiving stress experience, variable seasonal patterns of influenza in the tropics and sub-tropics has led some to raise uncertainty on the immunogenicity of influenza vaccines in these regions (Hsu et al. 1996 ; Thorpe et al. 2006 ). Furthermore, a study conducted in Taiwan showed that there were ethnic differences in immune responses to the hepatitis B vaccine, suggesting that host factors pertaining to ethnic origin could be a factor in determining immune responses to vaccination (Govaert et al. 1994) . As previous studies have evaluated the immune response to influenza vaccinations in relation to chronic stress (Kiecolt-Glaser et al. 1996; Kiecolt-Glaser et al. 2007) . However, in a critical review of studies that investigated the relationship between psychological stress and immune responses to immunization, Cohen et al. (2001) described methodological flaws in these studies that limit their usefulness. In particular, although evidence supports a relationship between psychological stress and secondary immune responses to immunization, the evidence is weak for the relationship between chronic stress and the primary immune response. Moreover, few studies have been conducted to assess the impact of chronic stress on both cell-and humoral-mediated immune responses to influenza vaccination. The present study thus investigated the effects of chronic stress, measured by a validated Caregiver Strain Index (CSI), on immunogenicity including both cell-mediated and humorally mediated immune responses to influenza vaccinations in Hong Kong Chinese elderly people. For the humorally mediated immune response to influenza vaccination, both primary and secondary responses to vaccination were also delineated by measuring the pre-vaccine antibody titers at baseline. Subjects were recruited from six general out-patient clinics and one geriatric clinic in the public health care system (Hospital Authority) in the New Territories East Cluster plus 13 non-government organizations and public housing estates located in Kowloon, Shatin, and Tai Po between July and September in 2006 by using a combination of advertisements and health education talks in community elderly centers. The criteria for a case being included were whether the person was a primary caregiver of whom their spouse had a diagnosis of either stroke, Parkinson's disease, or Alzheimer disease with a severe limitation of their activity daily living and whether they reported no other caregiving responsibilities at home. The respective criteria for the controls included whether a person had a partner who was alive and did not have a diagnosis of stroke, Parkinson's disease, or any other chronic illness and that they did not have any other caregiving responsibilities such as an elderly parent or a disabled child. Other relevant criteria were whether people were 60 years or above and whether they were able to give informed consent and were able to speak Cantonese. All had received an influenza vaccine in the year 2005 to standardize exposure to previous influenza vaccinations. Exclusion criteria were the presence of any current infectious diseases, fever (temperature, ≧37.5°C) at the baseline visit, known allergy to eggs or any component of the vaccines, uncontrolled coagulopathy or blood disorders contraindicating intramuscular injection, known congenital or acquired immunodeficiency (including HIV infection), whether people had received any immunosuppressive treatment, and any other disease known to alter immunity. Caregiver and control subjects were matched on sex and age. The study protocol was approved by the joint Chinese University of Hong Kong-New Territories East Cluster Ethics Committee. At baseline, eligible subjects were asked to provide demographic data that included age, sex, socioeconomic status measured by their monthly household income levels and levels of education, history of influenza vaccination, history of chronic medical conditions, diagnosis of the spouse's medical conditions, hours per day spent currently in caregiving, and years of caregiving. Medication use of subjects was validated, by asking them to present medications during the interview. Lifestyle factors such as cigarette smoking and alcohol consumption were recorded by validated methods (Chan et al. 1996) . Body mass index (BMI) and plasma albumin concentrations were measured to evaluate the nutritional status of the subjects. The level of physical activity in this study was determined by asking subjects about the number of minutes that they spent per week in physical exercise (Kohut et al. 2002) . The amount of physical exercise in minutes was recorded as most elderly people only performed mild to moderate levels of physical exercise. BMI and plasma albumin concentrations were used as indicators of nutritional status. The validated Chinese version of Global Measure of Perceived Stress Scale (PSS) (Cohen et al. 1983 ) and CSI (Chinese version) (Robinson 1983 ) were used to measure stress levels of the subjects. Depressive symptoms were measured by the validated Chinese version of the Geriatric Depression Scale-Short Form (GDS-15) (Lee et al. 1993) . The validated Chinese version of the Multidimensional Scale of Perceived Social Support (MSPSS) (Zimet et al. 1990 ) was used to measure the perceived social support from family, friends and significant others. A commercially available trivalent influenza vaccine (VaxiGrip, Sanofi Pasteur) For each case, the first blood sample was collected just before vaccination, and subsequent samples were collected at 6 and 12 weeks points after vaccination. All blood samples were drawn between 8:00 and 11:00 a.m. to control for diurnal variation. The presence of influenza-like illnesses or any respiratory infections were documented as these would affect the interpretation of influenza humoral and cellular immunity testes. Influenza vaccine strain-specific antibody titers were measured by the hemagglutination (HA) inhibition (HAI) method. Serial 2-fold dilution of virus (50 μl) was made with phosphate-buffered saline (PBS) in a U-bottom microtiter plate. A volume of 50-μl guinea pig red blood cells (RBC) suspension (0.75 %, v/v) was added to each well, following which the plate was manually agitated thoroughly. The cells were allowed to settle and incubate for 60 min at room temperature. The highest dilution of virus that causes complete hemagglutination is considered the HA titration end point. All patient sera were treated with a receptordestroying enzyme and incubated at 37°C overnight. The sera were then inactivated for 30 min at 56°C and diluted in physiological saline. Serial 2-fold dilution of each serum was prepared with PBS in a U-bottom microtiter plate. A viral dilution containing 4HA units/25 μl was added to each well and mixed thoroughly. The plate was incubated for 15 min at room temperature; 0.75 % guinea pig RBC suspension (50 μl) was then added to each well, and the plate was further incubated for 60 min at room temperature. The HAI titer is the reciprocal of the last dilution of antiserum that completely inhibits hemagglutination. In the analysis, the immune response of an influenza vaccine was evaluated by the titer of HAI acquired. Before the vaccination, no pre-vaccine immunity was defined as HAI titer of <1:10 and pre-vaccine immunity was defined as HAI titer of ≥1:10. Six weeks later, the responders in a no pre-vaccine immunity state were defined as HAI titer of ≥1:40, while the responders in a pre-vaccine immunity state were defined as HAI titer of ≥4-fold. For those responders, the duration of immunological protection was divided into categories of decline protection and persist protection, which were defined as HAI titer at 12 weeks