What is inside a General Purpose Operational Amplifier
The PNP who's collector node you have highlighted - let's call it Q1  (as well as the NPN directly above it on the schematic) are for current limiting at the output. The output current develops a voltage over the two resistors connected to OUT - IOUT*RSENSE. When this voltage exceeds a diode voltage, Q1 starts to turn on. The positive and negative current limits work differently, but the negative current limit which you have asked about specifically operates by sending a current back to the input and reducing the differential current generated by the input pair!