Acute GVHD is caused by-
Graft versus host (gvh) diseases

Graft versus host disease occurs in any situation in which immunologically competent cells or their precursors are transplanted into immunologically crippled patients and the transferred cells recognize alloantigens in the host.
Graft versus host disease occurs most commonly in the setting of allogeneic bone marrow transplantation but may also follow transplantation of solid organs rich in lymphoid cells (e.g. the liver) or transfusion of unirradiated blood.
Recipients of bone marrow transplants are immunodeficient because of either their primary disease or prior treatment of the disease with drugs or irradiation.
When such recipients receive normal bone marrow cells from allogeneic donors, the immunocompetent, T cells present in the donor marrow recognize the recipient’s HLA antigen as a foreign antigen and react against them. Both CD4+ and CD8+ T cells recognize and attack host tissues.
In clinical practice, GVH can be so severe that bone marrow transplants are done only between HLA matched donor and recipient.

Pathological changes in GVH diseases

There are three principal target tissues affected in GVHD: Skin, liver, and gut. GVHD may be acute or chronic:-

A) Acute GVHD

Acute GVHD occurs within 100 days (usually 10-50 days) of bone marrow transplantation. The manifestations of acute GVHD are

1. Skin

It is the most commonly affected tissue in acute GVHD. There is generalized rash (maculopapular).

Histological findings are
i. Perivascular mononuclear infiltrates.
ii. Vacuolar degradation of dermo-epidermal junction
iii. Dyskeratotic or eosinophilic bodies in the epidermis.
iv. Epidermolysis & bullae.
v. Denudation of epidermis (separation of epidermis from dermis),
2. Gut

The primary clinical manifestation of gut GVHD is diarrhoea and abdominal pain. There is lymphocytic infiltrate at the crypts with accompanied necrosis and drop out of crypt cells.

3. Liver

Lymphocytic infiltrates in the interlobular and marginal bile ducts are characteristic histopathologic findings. This results in hepatitis with necrosis of hepatocytes and bites duct epithelial cells. There is inflammation of the parenchyma and portal tracts. These findings lead to a clinically identifiable cholestatic picture.

B) Chronic GVHD

It occurs after 100 days of bone marrow transplantation. Manifestations are:-

1. Skin

Extensive cutaneous injury, with the destruction of skin appendages and fibrosis of the dermis.

2. Gut

Damage to GIT may result in necrosis, ulceration fibrosis and strictures.

3. Liver

The findings of liver damage are i) Portal tract inflammation ii) Selective bile duct destruction

iii. Endothelitis of the portal vein and hepatitis vein radicles, in which a subendothelial lymphocytic infiltrate lifts the endothelium from its basement membrane.
iv. Intrahepatic cholestasis
B lymphocyte
T lymphocyte
Macrophage
NKcell