In the PIC32MX demo main.c file, prvSetupHardware() calls portDISABLEINTERRUPTS(). Where do interrupts get enabled such that all the interrupts in the mainfull demo works? I do not see any call to portENABLE_INTERRUPTS() anywhere. Thanks for your help.

Every task has its own context, where interrupts are enabled where the task starts. Therefore interrupts because re-enabled automatically when the first task starts to execute.