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Collagen is the main structural protein in vertebrates. It plays an essential role in providing a scaffold for cellular support and thereby affecting cell attachment, migration, proliferation, differentiation, and survival. As such, it also plays an important role in numerous approaches to the engineering of human tissues for medical applications related to tissue, bone, and skin repair and reconstruction. Currently, the collagen used in tissue engineering applications is derived from animal tissues, creating concerns related to the quality, purity, and predictability of its performance. It also carries the risk of transmission of infectious agents and precipitating immunological reactions. The recent development of recombinant sources of human collagen provides a reliable, predictable and chemically defined source of purified human collagens that is free of animal components. The triple-helical collagens made by recombinant technology have the same amino acid sequence as human tissue-derived collagen. Furthermore, by achieving the equivalent extent of proline hydroxylation via coexpression of genes encoding prolyl hydroxylase with the collagen genes, one can produce collagens with a similar degree of stability as naturally occurring material. The recombinant production process of collagen involves the generation of single triple-helical molecules that are then used to construct more complex three-dimensional structures. If one loosely defines tissue engineering as the use of a biocompatible scaffold combined with a biologically active agent (be it a gene or gene construct, growth factor or other biologically active agent) to induce tissue regeneration, then the production of recombinant human collagen enables the engineering of human tissue based on a human matrix or scaffold. Recombinant human collagens are an efficient scaffold for bone repair when combined with a recombinant bone morphogenetic protein in a porous, sponge-like format, and when presented as a membrane, sponge or gel can serve as a basis for the engineering of skin, cartilage and periodontal ligament, depending on the specific requirements of the chosen application.

Female sex workers in Nairobi were prospectively evaluated for risk factors of incident Chlamydia trachomatis infection. Independent risk factors included cervical ectopy (P=.007), gonococcal infection (P=.002), human immunodeficiency virus (HIV) seropositivity (P=.003), HIV seroconversion (P=.001), and duration of prostitution (P=.002). Eighteen different C. trachomatis outer membrane protein (omp1) genotypes were identified, with the allelic composition of the C. trachomatis population changing significantly over time (P=.005). Seventeen of 19 reinfections > or = 6 months apart were with different C. trachomatis omp1 genotypes. Women with HIV infection had an increased proportion of visits with C. trachomatis infection (P=.001) and an increased risk of reinfection (P=.008). Overall, the data demonstrate significant fluctuations in the genotype composition of the C. trachomatis population and a reduced rate of same-genotype reinfection consistent with the occurrence of strain-specific immunity.

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