Gastrointestinal tract, immunological response

The neonate lacks the ability to mount a full immunological response, accordingly maternal IgG is transported across the placenta late in pregnancy and is also absorbed across the gastrointestinal tract from breast milk. Maternal IgA secreted into breast milk will also provide mucosal protection for the neonate. 

Histamine plays a central role in immunologic and anti-inflammatory responses, particularly in the immediate hypersensitivity response. Three subclasses of histamine receptors have been identified Hj, Hj, and Hj receptors. Hj receptors are involved in mediating increased vascular permeability, pruritus, coutraction of smooth muscle in the respiratory and gastrointestinal tracts, release of mediators of inflammation, and recruitment of inflammatory cells. Among other effects, Hj receptors mediate the negative feedback control of histamine synthesis and release and may play some defensive role against excess bronchoconstriction. H, and Hj receptors are both found primarily in bronchial smooth muscle in the human respiratory tract (40). 

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