What happens to the immune system after SCI?

Author: Sharon Jang | Reviewers: Phillip Popovich , Katherine Mifflin | Published: 2 September 2020 | Updated: 10 January 2025

Spinal Cord Injury Immune Depression Syndrome (SCI-IDS) is a condition that weakens the immune system after SCI. Weak evidence suggests that SCI-IDS commonly occurs among those with acute SCI. That said, there is also early evidence that SCI-IDS can persist and be present in those with chronic (>1 year) SCI. Although researchers are unsure why the immune system is weakened after SCI, hypotheses have been made:

  • SCI-IDS may be a self-defence mechanism that lowers the body’s immunity to prevent the body from attacking itself after the damage that has occurred in the spinal cord.
  • Many of the organs associated with the immune system, such as the spleen, thymus, and lymph nodes, are controlled by the sympathetic nervous system. These nerves are impaired when an individual sustains an injury at T6 or above. As a result, the immune system may not be as active.
Illustration accompanying What happens to the immune system after SCI?

A natural killer cell. The number of these cells is decreased after SCI.4

Weak evidence suggests that immune system changes may occur regardless of level of injury. For example, the amount of natural killer cells are reduced in adults with SCI, regardless of level of injury, in comparison to an able-bodied population. This reduces the body’s ability to fight off germs, which may cause infections, disease, and illnesses. Moreover, early animal research suggests that individuals with SCI may be more susceptible to viruses, such as the flu due to impairments in the body’s immunity. However, it is important to note that these findings have not yet been replicated in humans.

Illustration accompanying What happens to the immune system after SCI?

Although the immune system recovers after acute SCI, some (weak) evidence suggests that lowered immunity may extend into the chronic stage of SCI. One study investigated the genes responsible for programming and developing immune cells. The authors found that the genes that normally create natural killer cells are reduced, resulting in lower amounts of these germ-fighting cells throughout the body. A second study supported these findings, as individuals with SCI were found to have lower amounts of

natural killer cells

in their blood compared to an able-bodied population.

Having an SCI in combination with a weakened immune system has many implications for secondary complications. For example, after SCI many individuals may have difficulties with or be unable to effectively void urine, which encourages the growth of bacteria. This, in combination with a weakened immune system, may explain why urinary tract infections (UTIs) are a common secondary complication of SCI. Although SCI complications and a weakened immune system may contribute to many other secondary complications (e.g., UTI, pressure sores), this article will focus on infectious respiratory conditions that are common with SCI.

For more information, refer to our articles on UTIs and Pressure Injuries!