Vitamin A (continued)

What is Carotenoids?

Carotenoids consist of α- carotene and β-carotenene That can be found in dark green leafy vegetables , carrot , sweet potatoes ,mangoes and papayas and β-crytoxanthin that is found in oranges and tangerines. (De Pee et al ., 1995 ;west,2000)


How can Carotenoids (vitamin A) affect us?







Mucosal immunity
Vitamin A deficiency can impairs mucosal function tha lead to

• loss of cilia in the respiratory tract ,
  
• loss of microvilli in the gastrointestinal tract ,
  
• alteration in antigen- specific secretory immunoglobulin A(lgA) concentrations
  
• impairment of mucosal associated immune cell function .
  ( wolbach and Howe , 1925 ; Blackfan and Wolbach , 1933 ; Sweet and K’ang , 1935)
  CASE 1

• In vitamin A deficient BALB/c mice that were challenged with influenza A virus had a lower influenza specific IgA response than control mice. (Gangopadhyay et al ., 1996)
  
  
  

Natural killer cells (NK cells)

Vitamin A deficiency reduces the number of circulating Natural Killer cells and impairs NK cell cytolytic activity .NK cells attack virus and tumour cells that enhance our immune system.(Nauss and Newberne , 1985 ;Bowman et al ., 1990)
Children with acquired immune deficiency syndrome (AIDs) who receive two doses of oral vitamin A has large increases in the number of circulating NK cells , compared with children who received placebo ( Hussey et al ., 1996) Placebos exert an "expectancy" effect whereby an inert substance which is believed to be a drug has effects similar to the actual drug.

Neutrophiles

Neutrophils are non-specific immunity, because they phagocytose and kill bacteria, paracites ,virus-infected cells and tumour cells. Retinoic acid helps to mature neutrophils. If vitamin A deficient, the functions of neutrophils are impaired. (Lawson and Berliner, 1999)

T lymphocytes

Vitamin A modulate the balance between T-helper type 1 and T helper type 2 –like responses that improves lymphocyte responsiveness. (Carman et al ., 1992 ; cantorna et al ., 1994 ,1996) The effect of high-level dietary vitamin A on the shift to T-helper type 2- like responses in BALB/c mice has been used to explain the apparent lack of benefit of vitamin A supplementation for acute lower respiratory infections in human (Cui et al ., 2000)

B lymphocytes

Vitamin A impairs the growth ,activation and function of B lymphocytes.B lymphocytes have been shown to utilize a metabolite of retinol,14-hydroxy-4,14-retro-retinol,instead of retinoic acid that is a mediator for growth. (Bucket et al ., 1991)


Antibody response
Vitamin A deficiency impair the capacity to generate an antibody response to T-cell-dependent antigens(Smith and Hayes ,1987 ;Semba et al., 1992 ,1994 ; Wiedermann et al ., 1993a,b)
Vitamin A in resistance to infectious disease

Measles
Vitamin A supplementation reduce the chance of getting measles in infants and children (Markowitz et al ., 1989) Vitamin A supplementation modulate antibody responses to measles and increase total lymphocytes counts. Children receiving high dose of vitamin A supplementation (60mg RE upon admission and the following day) had significantly higher Ig G responses to measles virus and higher circulating lymphocyte counts during follow up , compared to children who receive placebo (Coutsoudis et al ., 1992)

Diarrhoeal disease
Diarrhoeal diseases among children are caused by Escherichia coli ,slamonella and vibrio cholera. Vitamin A supplementation for fortification has shown to reduce the morbidity and mortality of diarrhoeal disease among preschool children in developing countries. ( Sommer et al., 1984 ; Brillant et al ., 1985; DeSole et al ., 1987 ; Gujral et al ., 1993 ; Schaumberg et al ., 1996)