During adolescence, the human body undergoes various physical, physiological and immunological changes triggered and mediated by hormones, of which the most significant in females is 17--oestradiol (an oestrogen) and, in males, is testosterone. Oestradiol usually begins to act around the age of 10 and testosterone some months later. There is evidence that these steroids act directly not only on the primary and secondary sexual characteristics but also have an effect on the development and regulation of the immune system, including an increased risk in developing pubescent and post-pubescent autoimmunity. There is also some evidence that cell surface receptors on B cells and macrophages may detect sex hormones in the system.
What is the primary trigger for immunological changes in teens?
hormones

In the 19th century, the city was transformed by development relating to its status as a trading center, as well as by European immigration. The city adopted the Commissioners' Plan of 1811, which expanded the city street grid to encompass all of Manhattan. The 1825 completion of the Erie Canal through central New York connected the Atlantic port to the agricultural markets and commodities of the North American interior via the Hudson River and the Great Lakes. Local politics became dominated by Tammany Hall, a political machine supported by Irish and German immigrants.
The Erie Canal was finished being built in what year?
1825

Since the 1990s, there has been consolidation in New Zealand's state-owned tertiary education system. In the polytechnic sector: Wellington Polytechnic amalgamated with Massey University. The Central Institute of Technology explored a merger with the Waikato Institute of Technology, which was abandoned, but later, after financial concerns, controversially amalgamated with Hutt Valley Polytechnic, which in turn became Wellington Institute of Technology. Some smaller polytechnics in the North Island, such as Waiarapa Polytechnic, amalgamated with UCOL. (The only other amalgamations have been in the colleges of education.)
In what decade did New Zealand's tertiary education institutions begin consolidation?
1990s