Explain the Immune mechanisms - Physiology of Growth and Development

The immune system starts functioning in a baby through the inherited antibody (Ab) of the mother. But these antibodies keep breaking in the body. By another 1 ½ - 2 years, the normal level is attained. But there would be a lot of changes occurring till the thymus, an endocrine gland, becomes dysfunctional. This is attained only by the age of 8. Hence, we observe that babies are more prone to diseases like common cold, respiratory disorders, diarrohea etc. This is because of the poor development of immune mechanisms. Further, the infant is more prone to allergic responses to its own Ab. This is known as autoimmunity. The second contribution to these allergies can be due to the high absorptive power of the gastrointestinal tract. Here, many major proteins are absorbed fully which possibly might be leading to allergic reactions.