Question

Macrophages that can promote regeneration after a spinal cord injury should primarily be a. cytotoxic b. antigen presenting c. phagocytic d. naìve e. all of the above

Short answer

Answer: (c) Phagocytic macrophages

Step-by-step solution

Background on Macrophages

Macrophages are essential cells of the immune system that originate from monocytes. They can be found in various tissues and have diverse functions. Some of these functions include the clearance of dead cells, defense against pathogens, promoting tissue repair and regeneration, and orchestrating inflammatory response. Now, let's go through the options provided in the question:

Option A: Cytotoxic Macrophages

Cytotoxic macrophages are capable of directly lysing target cells. They are involved in the defense against pathogens, particularly virus-infected and tumor cells, but their role in spinal cord regeneration is not primary.

Option B: Antigen Presenting Macrophages

As antigen-presenting cells, these macrophages display antigens' fragments on their surface bound to MHC II complexes. Such a process initiates adaptive immune responses by activating T cells. While this is essential for the overall immune response, it does not directly contribute to regeneration after spinal cord injury.

Option C: Phagocytic Macrophages

Phagocytic macrophages are involved in the ingestion and elimination of dead cells, debris, and pathogens. They are crucial after an injury, as they help clear the damaged tissue and create an optimal environment for tissue repair and regeneration. They also release growth factors and cytokines that promote stem cells' proliferation, migration, and differentiation to regenerate tissue.

Option D: Naive Macrophages

Naive macrophages are macrophages that have not been exposed to any antigen or stimulatory compound yet. They stay in an inactive state and do not play a significant role in promoting regeneration after a spinal cord injury.

Option E: All of the Above

Considering the explanations provided for each option, it becomes evident that not all the macrophages listed have a primary role in promoting spinal cord regeneration after an injury.

Conclusion

From the given options, it's clear that phagocytic macrophages (c) play the most important role in promoting regeneration after a spinal cord injury. Therefore, the correct answer to the question is option (c) phagocytic macrophages.