Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Identification of TNF-alpha binding peptides from a D-amino acid hexapeptide library that specifically inhibit TNF-alpha binding to recombinant p55 receptor

Tumour necrosis factor alpha (TNF-alpha) is a pro-inflammatory cytokine with pleiotropic activity that binds to two transmembrane receptors. Its role in mediating the inflammatory response to injury or infection has been well documented and it has been shown to be a causative factor in rheumatoid arthritis, inflammatory bowel disease and septic shock. Using synthetic peptide libraries composed exclusively of D-amino acids, two distinct hexapeptide families that block the binding of TNF-alpha to its receptors were identified. In the deconvolution of the library, activity increased from submillimolar to the low micromolar range with the most active compound having an IC50 of 0.33 microM. With the aid of biotinylated constructs of these hexapeptides it was possible to demonstrate that their antagonistic effect is due to specific binding to TNF-alpha and not to its receptor.     

Anti-IL-13 monoclonal antibody inhibits airway hyperresponsiveness, inflammation and airway remodeling

Asthma is a chronic inflammatory disease characterized by reversible bronchial constriction, pulmonary inflammation and airway remodeling. Current standard therapies for asthma provide symptomatic control but fail to target the underlying disease pathology. Furthermore, no therapeutic agent is effective in preventing airway remodeling. Interleukin 13 (IL-13) is a pleiotropic cytokine produced mainly by T cells. A substantial amount of evidence suggests that IL-13 plays a critical role in the pathogenesis of asthma. Therefore, a neutralizing anti-IL-13 monoclonal antibody could provide therapeutic benefits to asthmatic patients. To test the concept we have generated a neutralizing rat anti-mouse IL-13 monoclonal antibody, and evaluated its effects in a chronic mouse model of asthma. Chronic asthma-like response was induced in ovalbumin (OVA) sensitized mice by repeated intranasal OVA challenges. After weeks of challenge, mice developed airway hyperresponsiveness (AHR) to methacholine stimulation, severe airway inflammation, hyper mucus production, and subepithelial fibrosis. When given at the time of each intranasal OVA challenge, anti-IL-13 antibody significantly suppressed AHR, eosinophil infiltration, proinflammatory cytokine/chemokine production, serum IgE, and most interestingly, airway remodeling. Taken together, these results strongly suggest that a neutralizing anti-human IL-13 monoclonal antibody could be an effective therapeutic agent for asthma.     

Sequence-function analysis of the K+-selective family of ion channels using a comprehensive alignment and the KcsA channel structure

Sequence-function analysis of K(+)-selective channels was carried out in the context of the 3.2 A crystal structure of a K(+) channel (KcsA) from Streptomyces lividans (Doyle et al., 1998). The first step was the construction of an alignment of a comprehensive set of K(+)-selective channel sequences forming the putative permeation path. This pathway consists of two transmembrane segments plus an extracellular linker. Included in the alignment are channels from the eight major classes of K(+)-selective channels from a wide variety of species, displaying varied rectification, gating, and activation properties. Segments of the alignment were assigned to structural motifs based on the KcsA structure. The alignment's accuracy was verified by two observations on these motifs: 1), the most variability is shown in the turret region, which functionally is strongly implicated in susceptibility to toxin binding; and 2), the selectivity filter and pore helix are the most highly conserved regions. This alignment combined with the KcsA structure was used to assess whether clusters of contiguous residues linked by hydrophobic or electrostatic interactions in KcsA are conserved in the K(+)-selective channel family. Analysis of sequence conservation patterns in the alignment suggests that a cluster of conserved residues is critical for determining the degree of K(+) selectivity. The alignment also supports the near-universality of the "glycine hinge" mechanism at the center of the inner helix for opening K channels. This mechanism has been suggested by the recent crystallization of a K channel in the open state. Further, the alignment reveals a second highly conserved glycine near the extracellular end of the inner helix, which may be important in minimizing deformation of the extracellular vestibule as the channel opens. These and other sequence-function relationships found in this analysis suggest that much of the permeation path architecture in KcsA is present in most K(+)-selective channels. Because of this finding, the alignment provides a robust starting point for homology modeling of the permeation paths of other K(+)-selective channel classes and elucidation of sequence-function relationships therein. To assay these applications, a homology model of the Shaker A channel permeation path was constructed using the alignment and KcsA as the template, and its structure evaluated in light of established structural criteria.     

Anti-TNF-alpha antibody allows healing of joint damage in polyarthritic transgenic mice

Anti-tumor-necrosis-factor-alpha (TNF-alpha) monoclonal antibody was used to treat Tg197 transgenic mice, which constitutively produce human TNF-alpha (hTNF-alpha) and develop a progressive polyarthritic disease. Treatment of both young (7- or 8-week-old) and aged (27- or 28-week-old) mice commenced when at least two limbs showed signs of moderate to severe arthritis. The therapeutic efficacy of anti-TNF-alpha antibody was assessed using various pathological indicators of disease progression. The clinical severity of arthritis in Tg197 mice was significantly reduced after anti-TNF-alpha treatment in comparison with saline-treated mice and in comparison with baseline assessments in both young and aged mice. The treatment with anti-TNF-alpha prevented loss of body weight. Inflammatory pathways as reflected by elevated circulating hTNF-alpha and local expression of various proinflammatory mediators were all diminished by anti-TNF-alpha treatment, confirming a critical role of hTNF-alpha in this model of progressive polyarthritis. More importantly, the amelioration of the disease was associated with reversal of existing structural damage, including synovitis and periosteal bone erosions evident on histology. Repair of cartilage was age dependent: reversal of cartilage degradation after anti-TNF-alpha treatment was observed in young mice but not in aged mice.     

A grafting approach to obtain site-specific metal-binding properties of EF-hand proteins

The EF-hand calcium-binding loop III from calmodulin was inserted with glycine linkers into the scaffold protein CD2.D1 at three locations to study site-specific calcium binding properties of EF-hand motifs. After insertion, the host protein retains its native structure and forms a 1:1 metal-protein complex for calcium and its analog, lanthanum. Tyrosine-sensitized Tb3+ energy transfer exhibits metal binding and La3+ and Ca2+ compete for the metal binding site. The grafted EF-loop III in different environments has similar La3+ binding affinities, suggesting that it is largely solvated and functions independently from the host protein.     

Discovery and mechanism of ustekinumab: A human monoclonal antibody targeting interleukin-12 and interleukin-23 for treatment of immune-mediated disorders

Monoclonal antibody (mAb) therapy was first established upon the approval of a mouse antibody for treatment of human acute organ rejection. However, the high incidence of immune response against the mouse mAb restricted therapeutic utility. Development of chimeric, “humanized” and human mAbs broadened therapeutic application to immune-mediated diseases requiring long-term treatment. Indeed, mAb therapeutics targeting soluble cytokines are highly effective in numerous immune-mediated disorders. A recent example is ustekinumab, a first-in-class therapeutic human immunoglobulin (Ig) G₁ kappa mAb that binds to the interleukins (IL)-12 and IL-23, cytokines that modulate lymphocyte function, including T-helper (Th) 1 and Th17 cell subsets. Ustekinumab was generated via recombinant human IL-12 immunization of human Ig (hu-Ig) transgenic mice. Ustekinumab binds to the p40 subunit common to IL-12 and IL-23 and prevents their interaction with the IL-12 receptor β1 subunit of the IL-12 and IL-23 receptor complexes. Ustekinumab is approved for treatment of moderate-to-severe plaque psoriasis and has demonstrated efficacy in Crohn disease and psoriatic arthritis. The clinical characterization of ustekinumab continues to refine our understanding of human immune pathologies and may offer a novel therapeutic option for certain immune-mediated diseases.Key words: ustekinumab, psoriasis, monoclonal antibody, interleukin-12/23p40