This study assesses the utility of saliva samples to monitor the time course of the acute-phase response to different viruses in pigs under field conditions by using time-resolved immunofluorometric assays (TR-IFMA). A total of 30 pigs from three different farms, located in Southeast Spain, were used. Farm 1 had outbreaks of porcine circovirus type 2, farm 2 had infections with porcine reproductive and respiratory syndrome virus and farm 3 had concomitant infections with both viruses. Serology was used to determine the time of seroconversion of pigs to two different pathogens. The levels of two acute-phase proteins (APPs), C-reactive protein (CRP) and haptoglobin (Hp), were measured in saliva and serum samples and compared with pig's serology. Kinetic curves of both APPs across the study obtained in saliva samples were similar to those of serum, with R of 0.68 and 0.78 for CRP and Hp, respectively. The median CRP and Hp concentrations in saliva were higher around the theorized time of infection, according to previous experimental studies, and at seroconversion of animals. CRP increments were apparent 1 week before the increments obtained in Hp. These findings indicate that salivary APP concentrations, by using TR-IFMA, can be used in longitudinal studies as non-invasive early indicators of health status.

Inflammation influences the assessment of nutritional status. For example, inflammation reduces plasma retinol concentrations and vitamin A deficiency is overestimated. Conversely inflammation increases plasma ferritin concentrations and Fe deficiency is underestimated. Blood samples were obtained from 163 free-living HIV-1-infected adults, not on continuous medication, anti-retroviral drugs or micronutrients, not unwell and who had not reached WHO stage IV of HIV/AIDS. We used four markers of inflammation, C-reactive protein (CRP), α1-acid glycoprotein (AGP), α1-antichymotrypsin and erythrocyte sedimentation rate but mainly CRP and AGP were used to separate the subjects into four groups: ‘healthy’ where both CRP and AGP were normal; ‘incubation phase’ where CRP was elevated; ‘early convalescence’ where AGP and CRP were elevated and ‘late convalescence’ where only AGP was elevated. Correction factors were calculated to remove the influence of inflammation from each biomarker and group where inflammation was present and the data are shown before and after recalculation. The correction increased median plasma retinol concentrations of the whole group from 1·16 to 1·33 μmol/l, comparable with values (mean 1·29 μmol/l) in HIV-negative Kenyan women. Median ferritin concentrations fell by about 50 % in both sexes and the number of women with plasma ferritin concentrations ≤ 12 μg/l increased from eleven to twenty. The correction also increased plasma carotenoids and Hb but not α-tocopherol concentrations. We suggest that the method described to remove the influence of inflammation from nutritional biomarkers should be generally applicable in apparently healthy people and prevents discarding valuable data because of mild inflammation. The method does now need to be tested in other populations.

Inflammatory processes are involved in the pathogenesis of the most common chronic non-communicable diseases and may also play an important initiating role in their development. Only recently have inflammatory markers been included in epidemiological studies focusing on nutritional status, body composition and physical activity. We are just starting to understand how different lifestyles can determine basal levels of inflammatory biomarkers in early ages. This review aims to summarise what is known about the relationships between lifestyle-related determinants (focusing on overweight, physical activity and dietary habits) and inflammatory markers in apparently healthy young populations. Obesity is the most widely studied determinant. Several large-scale studies have now demonstrated that healthy young subjects with more body fat or higher BMI have moderately higher concentrations of inflammatory markers than their leaner peers, supporting the idea that obesity should be considered as a state of chronic low-grade inflammation. Less data is available to allow us to elucidate how physical activity/fitness or dietary patterns may have a direct effect on inflammation in apparently healthy, disease-free young populations.

The objectives of the present study were to identify predictors of serum retinol concentration as well as to assess the prevalence of low serum retinol concentration, in both the whole population after correcting for the effect of serum C-reactive protein (CRP) (using multiple categories), and the healthy subgroup. A cross-sectional study of 579 apparently healthy children, aged 3–7 years from a Dhaka slum, Bangladesh, was conducted. The effects of age, gender, serum CRP and α1-antichymotrypsin, reported morbidity (during the previous 2 weeks), Ascaris lumbricoides and Trichuris trichiura infections, parental education, wasting, stunting and underweight on serum retinol were estimated using multiple linear regression. The mean serum retinol concentration was 0·84 (sd 0·27) μmol/l. Elevated serum CRP levels, reported diarrhoea, reported nasal discharge and T. trichiura infection were negative predictors of serum retinol, whereas maternal education was a positive predictor. Compared with a serum CRP level of <1 mg/l, CRP levels of 2 to <5, 5 to <10 and ≥10 mg/l were associated with 0·12, 0·16 and 0·32 μmol/l lower serum retinol, respectively. The prevalence of low serum retinol (<0·70 μmol/l) fell from 31·2 % to 15·6 % in the whole population, after correcting for the effect of CRP, and was 20·1 % in the healthy subgroup (CRP <2 mg/l). The prevalence of low serum retinol was high but overestimated due to the effect of CRP. Interventions are needed to address low serum retinol in Bangladesh. Controlling diarrhoea, nasal discharge and T. trichiura infection and improving maternal education may be important interventions. The use of multiple categories of acute-phase proteins and cut-off values that indicate elevated levels need further research.

Using the World Health Organization criterion, the prevalence of sub-clinical vitamin A deficiency can be assessed using plasma retinol concentrations <0·7 μmol/l. However, plasma retinol can be depressed by infection; thus, the use of this criterion alone may overestimate deficiency. In the present study, we investigated the usefulness of the acute-phase proteins (APP) α1-antichymotrypsin (ACT) and α1-acid glycoprotein (AGP), plasma carotenoids and anthropometric and gestational indices to interpret plasma retinol in the blood of 192 apparently healthy Nigerian neonates collected randomly during days 1–20 postpartum. The mean weight (2·64 kg) and length (0·458 m) of the neonates and plasma concentrations (geometric mean, μmol/l) of retinol (0·54), α-carotene (0·072), ß-carotene (0·076) and lutein (0·080) were low. The prevalence of vitamin A deficiency was 72 %, indicating a severe public health problem. Babies who were of low birth weight (P<0·003) or premature and low birth weight (P<0·023) had significantly lower retinol concentrations than full-term normal weight babies. Thirty-two neonates had abnormal ACT and forty-four abnormal AGP concentrations. Positive correlations between retinol and ACT (r 0·186, P=0·05) and AGP (r 0·31, P=0·0001) during days 1–5 may be due to the increasing plasma retinol from maternal milk and a coincidental increasing capacity to synthesise APP. Subsequently, negative correlations between retinol and ACT (r −0·28, P=0·02) and AGP (r −0·29, P=0·018) from day 6 onwards reflected the continuing increase in plasma retinol, but no further increase in the APP. Overall, weight, ACT, lutein and age explained 30 % of the variance in retinol, but lutein was the most significant (r2 0·18, P<0·0001). Hence, the distribution of plasma retinol concentrations in this group of neonates was more strongly linked with nutrition (via the surrogate marker lutein) than infection.