## 4 Discussion
This timing of the innate component enables the newborn to combat potential pathogens effectively from birth onwards. The results of the present study show that the baseline concentration of cathelicidin is higher in young infants than in newborns in contrast to those of alpha- and beta-defensin, suggesting that not all innate immunity components develop in the same time-dependent way. This phenomenon might be explained by a different phase in the immunological development of the child as mentioned above. No such significant differences were observed for s-IgA levels, representing the adaptive component. At birth, as demonstrated [12], consumption of the postbiotic FM-CBA L74 led to an increase in s-IgA levels to similar values as those of breastfed newborns, in contrast to that observed in the placebo. Compensation in this might take place: newborns with high levels of immune factors at the start should avoid even higher levels to minimize unwanted side effects, resulting in a negative association with starting levels. At 1-4 years old the immune system is readily developed, especially in the humoral part of immunity [25], leaving no room for further improvement in factors, except when stimulated, as in the present study by consumption of the postbiotic cow's milk drink: the positive association between the increases and the start levels is only observed in this group and not in the placebo. Another factor of importance for the baseline concentrations of immune markers is the development of the microbiome, which depends, if applicable, on the selection of the infant formula [26]. The diet of the mother during pregnancy is known to affect this composition [27] as well as the general status of the mother [28]. Overall, the composition of the microbiome is affected by many other factors, such as method of delivery, maternal diet, introduction to solid food, etc. [29]. The relationship between microbiome and the concentration of immune factors at any age during development needs further attention. Is the increase in the concentration of the various factors as established by the consumption of the intervention potentially harmful to the host? The actual concentration of the fecal parameter 3 months after the start of consumption of the intervention product is far below the levels observed during inflammation/infection, such as \(\beta\)-defensin in children with inflammatory bowel diseases [30]: in children suffering from ulcerative colitis a median level of 356 ng/g was obtained. The same holds true in newborns. A study in preterm neonates fed with a combination of breast milk or formula, or combinations hereof, from complete breast milk to complete formula feed, \(\beta\)-defensin concentrations of about 340 ng/mL in neonates on predominant formula milk were encountered [31]. Similar observations were found for s-IgA. A study on the impact of various formulas on fecal s-IgA levels in healthy infants [32] showed that in the control group (after 26 wks of intervention) concentrations of 377 \(\mu\)g/g versus 729 \(\mu\)g/g in the GOS/FOS group was observed. The above shows that concentrations as yielded in the present study due to the intervention with the postbiotic cow's milk drink, were substantially lower than documented for the various conditions as mentioned in the various studies above. It is hypothesized that the levels in the present study are representative for a state of vigilance optimizing the immune system in newborns and young infants, not to be compared with those during a state of infection/inflammation with unwanted side effects. Is the increase in concentrations as observed in the present study associated with a beneficial physiological effect? In the study on newborns [12], consumption for 3 months of the fermented cow's milk yielded s-IgA levels similar to those observed in newborns on breast milk whereas those in the control group remained significantly lower: consumption of the intervention clearly led to an improvement in the immune status in these newborns.