Mathias Jul Jørgensen
|Jørgensen, Mathias Jul. 2010. Understanding the immunological effects of vitamin A supplementation. Bandim Health Project, Statens Serum Institut. Faculty of Health Sciences, University of Copenhagen. 149 p.
||Vitamin A is essential for protection against infectious diseases as is seen by the severe implications of being vitamin A deficient. Vitamin A supplementation (VAS) has been observed to have a major impact on the mortality of children in low-income countries, although the exact biological mechanisms are unknown. The Bandim Health Project has repeatedly published results revealing differential mortality effects of VAS depending on the sex and vaccination status of the recipient. In particular, a negative interaction between VAS and diphtheria-tetanus-pertussis (DTP) vaccine has been observed. The work included in the present thesis has been focused on investigating the immunological mechanisms behind these observations in a number of different ways.
First, animal studies were initiated. We chose an existing model of murine cerebral malaria and modified it slightly in order to investigate how the progression of disease was affected by pretreatment with VAS and DTP vaccination. We found that the combined pretreatment with VAS and DTP vaccination resulted in increased parasitemia levels compared with controls. No effect was seen on time to death. In the same model we investigated how the pretreatment with VAS/DTP influenced plasma cytokine levels after infection. We found that for mice, which developed cerebral malaria, the VAS/DTP-group had lower cytokine concentrations than controls. The opposite tendency was seen for mice that did not develop cerebral malaria. The studies corroborate that VA8 given DTP can have detrimental consequences and that the effect may depend on the underlying pathophysioiogy.
Second, we analyzed an existing dataset to examine how neonatal affected the differential leukocyte counts and in vitro cytokine response 6 weeks tater in a whole blood culture assay. VAS increased monocyte frequencies. At the same time the spontaneous TNF-α production was decreased among VAS recipients compared with placebo recipients. We analyzed data stratified by sex and DTP vaccination status and discovered statistically significant three-way interactions for the spontaneous TNF-α and IL-10 production; VA8 was associated with a decrease in TNF-α and IL-10 production for girls without DTP vaccine and boys with DTP vaccine.
Within the same study we investigated if Single Nucleotide Polymorphisms (SNPs) in cytokine genes and TLR4 affected the in vitro cytokine response. For the investigated panel of SNPs the genetic background of the study population did not appear to be a major determinant for in vitro cytokine production. We did however observe significant interactions between VAS and genotype and these appeared to be most pronounced among boys.
For the majority of children this will mean that they receive VAS together with measles vaccine. Within this trial, a subgroup of children was invited to participate in an immunological study. We aimed to examine the immunological effects of receiving VAS or measles vaccine. We looked at in vitro cytokine production at baseline and 6 weeks after supplementation using a whole blood culture protocol. We evaluated the vitamin A status at these points in time via plasma concentrations of retinol binding protein with potential adjustment for ongoing inflammation measured via plasma levels of C-reactive protein. Finally, we performed on-site automated hematological analysis on participants thus adding a white blood cell count and a 5-point differential count to the data.
The study showed no overall effects of with measles vaccine on differential counts, but there were significant interactions between VAS and sex for several cell types. We noted that main effects of VAS on cytokine production were seen for spontaneous IL-10 production along with TNF-α and IL-10 production after stimulation with PAM and OPV. VAS was in all instances associated with an increase in cytokine production. The results corroborate that VAS provided with MV has a general impact on the immune system, which may depend on the sex of the recipient. Our results may point to an increased responsiveness of the innate immune system after VAS along with a general anti-inflammatory effect.