● Isolation, death anxiety, lack of freedom and meaninglessness can predict anxiety symptoms.
● Prediction of anxiety symptoms based on confrontation with isolation and responsibility can be moderated by mature and immature defense mechanisms. 
● Prediction of anxiety symptoms based on confrontation with death anxiety, isolation, and responsibility can be moderated by neurotic defense mechanism.

Plain Language Summary 
Existential concerns  (death, freedom, meaninglessness, and isolation ) are common in all humans. This confrontation naturally produces anxiety. If the anxiety is higher than normal, a variety of mental disorders may develop. Hence, it is important to examine how we confront with existential concerns. Different defense mechanisms reflect how we confront with existential concerns. Defense mechanisms are strategies that we use against problems. Some of them including mature defense mechanism (e.g. humor and optimism) can lead to our health, while other mechanisms like immature and neurotic defense mechanisms (e.g. denial of problems) can lead to various psychological problems. In this study, we found that mature defense mechanisms can reduce the level of anxiety created by isolation and responsibility. In contrast, other defense mechanisms may lead to higher anxiety. There, we can protect ourselves from the burden of responsibility and isolation by using mature defense mechanism. In other words, we can reduce the burden of responsibility, isolation and death anxiety by reducing the use of other defense mechanisms.