**Core Concept**
The histocompatibility reaction is a process where the immune system recognizes and responds to foreign antigens, leading to graft rejection. This process involves T-lymphocytes, specifically a subset that plays a crucial role in recognizing and responding to histocompatibility antigens. The correct type of T-lymphocyte responsible for this reaction involves the recognition of peptide fragments presented by major histocompatibility complex (MHC) molecules on antigen-presenting cells.

**Why the Correct Answer is Right**
The correct type of T-lymphocyte responsible for the histocompatibility reaction is the CD4+ T-lymphocyte, also known as the helper T-lymphocyte. These cells recognize peptide fragments presented by MHC class II molecules on antigen-presenting cells, such as dendritic cells and macrophages. This recognition leads to the activation of CD4+ T-lymphocytes, which then orchestrate the immune response by activating other immune cells, such as B-lymphocytes and cytotoxic T-lymphocytes. The recognition of histocompatibility antigens by CD4+ T-lymphocytes is a critical step in the histocompatibility reaction, leading to graft rejection.

**Why Each Wrong Option is Incorrect**
**Option A:** CD8+ T-lymphocytes are primarily responsible for recognizing and responding to peptide fragments presented by MHC class I molecules, which are not directly involved in the histocompatibility reaction.
**Option B:** B-lymphocytes are responsible for recognizing and responding to antigens, but they do not play a direct role in the histocompatibility reaction.
**Option C:** Natural killer cells are a type of lymphocyte that can recognize and respond to stressed or infected cells, but they are not directly involved in the histocompatibility reaction.

**Clinical Pearl / High-Yield Fact**
The histocompatibility reaction is a critical process in transplantation medicine, where the recognition of histocompatibility antigens by CD4+ T-lymphocytes leads to graft rejection. Understanding this process is essential for optimizing immunosuppressive therapy and improving graft survival in transplant patients.

**Correct Answer:** C. CD4+ T-lymphocytes