Affinity-coupled CCL22 promotes positive selection in germinal centres.

Antibody affinity maturation depends on positive selection in germinal centres (GCs) of rare B cell clones that acquire higher-affinity B cell receptors via somatic hypermutation, present more antigen to follicular helper T (TFH) cells and, consequently, receive more contact-dependent T cell help1. As these GC B cells and TFH cells do not maintain long-lasting contacts in the chaotic GC environment2-4, it is unclear how sufficient T cell help is cumulatively focused onto those rare clones. Here we show that, upon stimulation of CD40, GC B cells upregulate the chemokine CCL22 and to a lesser extent CCL17. By engaging the chemokine receptor CCR4 on TFH cells, CCL22 and CCL17 can attract multiple helper cells from a distance, thus increasing the chance of productive help. During a GC response, B cells that acquire higher antigen-binding affinities express higher levels of CCL22, which in turn 'highlight' these high-affinity GC B cells. Acute increase or blockade of TFH cells helps to rapidly increase or decrease CCL22 expression by GC B cells, respectively. Therefore, a chemokine-based intercellular reaction circuit links the amount of T cell help that individual B cells have received recently to their subsequent ability to attract more help. When CCL22 and CCL17 are ablated in B cells, GCs form but B cells are not affinity-matured efficiently. When competing with wild-type B cells in the same reaction, B cells lacking CCL22 and CCL17 receive less T cell help to maintain GC participation or develop into bone-marrow plasma cells. By uncovering a chemokine-mediated mechanism that highlights affinity-improved B cells for preferential help from TFH cells, our study reveals a principle of spatiotemporal orchestration of GC positive selection.

Insulin-like growth factor-1 and neurotrophin-3 gene therapy prevents motor decline in an X-linked adrenoleukodystrophy mouse model.

X-linked adrenoleukodystrophy (X-ALD) is the most common inherited peroxisomal disorder characterized by a progressive demyelination of the central nervous system. The marked loss of myelin and oligodendrocytes observed in the disease prompted us to evaluate the therapeutic potential of insulin-like growth factor-1 and neurotrophin-3, two potent inducers of myelin formation and oligodendrocyte survival. Viral vectors engineered to produce insulin-like growth factor-1 or neurotrophin-3 were administrated into the cerebrospinal fluid of an X-linked adrenoleukodystrophy mouse model. We show that viral-based, long-lasting delivery of insulin-like growth factor-1 and neurotrophin-3 significantly halts the progression of the disease and leads to potent protective effect against the demyelination process. Ann Neurol 2009;66:117-122.