How are MPO cables connected?

To establish an MPO connection between two MPO cables, an MPO adapter is a must and the connectors should have opposing types. Which means only male to female connection is possible, not male-male or female-female. If a female connector is used on both sides of the adapter the performance would be very low because without male pins the fibers would not be aligned. On the other hand using two male connectors is not possible and might damage the connectors.