IL-8 is a chemokine which mediates in chemotaxis and in the activation of neutrophils.

Immature lymphocytes which are destined to become T-cells travel from the bone marrow to the thymus where they differentiate to immunocompetence and are educated to recognize peptides derived from foreign antigens presented by self MHC molecules. Thus in a thymectomized animal, this process cannot take place.

All of the immunoglobulin gene loci (heavy, kappa light, lambda light) exhibit allelic exclusion, as do all of the T-cell receptor gene loci, except the alpha chain. Thus, a B-cell is able to express only one light and one heavy chain specificity.

IgG is the only class of immunoglobulin which is acquired by the neonate by placental transfer from the mother. This process is dependent upon Fc structures specific to this Ig class. The maternal IgG is catabolized with a half-life of approximately 23 days.

Clusters of responding T-cells surrounding an antigen-presenting cell mutually support activation and proliferation.

LFA-1 is a member of the integrin family, molecules concerned with leukocyte binding to endothelial cells and to extracellular matrix proteins. The VLA molecules are also members of the integrin superfamily.

The peptide in the MHC groove is derived from intracellular proteins, either endogenous or exogenously derived.

The cytosolic proteins are cleaved to small peptides in the proteasome complex before they are transported by the TAP-1/2 molecules into the endoplasmic reticulum.

About ten per cent of the peptides generated by the housekeeping proteasome are 8–9 residues in length, but the immunoproteasome is thought to be specialized to produce a greater proportion of peptides of this length which is optimal for insertion into the MHC class I groove.

Cortical epithelial cells may be relatively inefficient antigen processors and only deliver a weak signal which induces proliferation rather than deletion of immature thymocytes.

Neutrophils are chemotactically attracted to the site of inflammation by C5a and mast cell chemotactic factors such as leukotriene B4.

This increases the risk of monochorionic monoamniotic (MCMA) twins by 5 times;  the reasons for this are poorly understood.

Pregnancies that share the placenta and amnion are at highest risk of adverse outcome because of risk of twin-to-twin transfusion syndrome and cord entanglement.

Unusually for a vein, the umbilical vein carries oxygenated blood from the placenta to the IVC via the ductus venosus. Umbilical cord pH is usually higher in the vein than in the artery.

It is important to monitor congenital abnormalities to understand their aetiology. Preconception folic acid supplementation to prevent spina bifida shows the benefit of recognizing high-risk groups.