How can kidney disease affect the immune system?

Plenty of reasons. If your kidneys are losing protein in your urine (proteinuria), this can affect the production of antibodies to fight infections. If your kidney disease is a result of uncontrolled diabetes, elevated blood sugars can lower the immune response to infections. Finally, if one is on dialysis, great care must be taken to keep the dialysis site sterile as this is often a source of infections.
Decrease it! All chronic body illnesses weaken the immune system. Physical and mental--- makes no different. Weakens the immune response!

Related Questions

How does kidney disease actually affect the immune system?

Lowers immunity . Kidney diseases usually lowers someone's immunity as evidenced by the high risk of these patients to develop infections ( pneumonia, urine infection etc) and their lack to respond appropriately to vaccinations ( hepatitis ....). Read more...
Immune function. You can have increased immune susceptibility but the body usually compensates over the long term to make up for this loss. And often times it could be the immunosuppressant medications that make you more susceptible to infection. Read more...