P. Metcalfe

Use of leucocyte-poor blood components and HLA-matched-platelet donors to prevent HLA alloimmunization

Summary. Recent studies have shown that the incidence of alloimmunization due to repeated platelet transfusions from random donors may be reduced by the use of leucocyte‐poor blood components. These results were confirmed by this study, where 16% of patients with acute leukaemia undergoing initial chemotherapy and receiving leucocyte‐poor blood components developed lymphocytotoxic antibodies, compared with 48% of patients in a control group receiving standard (non‐leucocyte‐depleted) blood components. In a third group, who received leucocyte‐poor blood components and HLA‐matched platelets, none of the patients developed lymphocytotoxic antibodies. There was a low incidence of platelet‐specific antibodies (8%) but no difference between the three groups. Improved methods of removing leucocytes from blood components appear to offer the best approach for minimizing HLA alloimmunization, as the provision of HLA‐matched platelet donors for prophylactic platelet support of all patients is not feasible.

Incidence and mechanism of neutropenia and thrombocytopenia in patients with human immunodeficiency virus infection

The incidence of lymphopenia, thrombocytopenia and neutropenia was studied in 105 homosexual men with HIV infection. Lymphopenia was common in patients with AIDS (75%), but its incidence in PGL (24%) was not significantly different from that in asymptomatic anti‐HIV positive (15%) homosexual men. Neutropenia and thrombocytopenia were found in patients with AIDS or PGL. but not in asymptomatic anti‐HIV positive homosexuals. The study suggests that the neutropenia and thombocytopenia in these patients were due to autoimmune destruction of neutrophils and platelets.

Relative Importance of Immune and Non-Immune Causes of Platelet Refractoriness

In this prospective study, 26 consecutive patients being treated for haematological malignancies receiving standard (i.e. non‐leucocyte‐depleted) blood components were observed for the development of refractoriness to platelet transfusions. One hundred and sixteen of the 266 (44%) platelet transfusions failed to produce a satisfactory response. In 102/116 (88%), the poor response was in the presence of non‐immune factors known to be associated with platelet refractoriness. Non‐immune factors were present alone in 78/116 (67%), and in combination with immune factors in a further 24/116 (21%). Immune factors (HLA and platelet‐specific antibodies) were present during 29/116 (25%) of unsuccessful platelet transfusions. Statistical analysis confirmed that platelet refractoriness was significantly associated with the presence of nonimmune factors. The non‐immune factors associated with refractoriness were often multiple, most frequently a combination of fever, infection and antibiotic therapy. This study provides evidence that immune mechanisms were not the predominant cause of platelet refractoriness in the patient population studied. It also suggests that measures for the prevention of HLA alloimmunisation, such as leucocyte depletion, may have a limited impact in reducing the incidence of refractoriness to platelet transfusions.

HPA‐1 typing by PCR amplification with sequence‐specific primers (PCR‐SSP): a rapid and simple technique

Summary. A DNA‐based method was developed to genotype donors for the human platelet antigens HPA‐la and ‐1b. Sequence‐specific primers (SSP) were used in the polymerase chain reaction (PCR) which allowed the HPA‐la/la. ‐lb/lb and ‐la/lb genotypes to be determined by PCR alone, no second analytical stage was required. 10 donors were tested by PCR‐SSP and the results were concordant with serological phenotyping and independent DNA analysis.

Antenatal screening for fetal alloimmune thrombocytopenia : the results of a pilot study

Summary. Feto‐maternal incompatibility for the human platelet antigen HPA‐la is an important cause of severe fetal thrombocytopenia. The incidence is 1 in 1000‐2000 pregnancies, which is more common than other conditions for which screening is presently carried out. Antenatal diagnosis and management are now available, but only for subsequent siblings following diagnosis of a previously affected infant. This study describes a pilot prospective screening programme for the antenatal detection of feto‐maternal alloimmune thrombocytopenia (FMAIT) due to HPA‐la incompatibility. 3473 women were typed for HPA‐la using a method designed for large‐scale typing. 71 women found to be HPA‐la negative were further tested for HLA‐DR52a as a risk factor for alloimmunization. All women were monitored for the development of anti‐HPA‐la throughout pregnancy and a cord full blood count was taken at delivery. Two affected pregnancies were found and treated: a singleton pregnancy was treated antenatally and a twin pregnancy after delivery. The study showed that screening for FMAIT could be established within the pre‐existing antenatal red cell serology programme. It was concluded that screening should be based on platelet typing and offered regardless of parity. Further stratification, combining DR52a typing and HPA‐la antibody screening, although focusing on the group of women at greater risk, may not identify all affected pregnancies. Confirmation of the diagnosis and severity of FMAIT continues to depend on fetal blood sampling during pregnancy or cord blood samples after birth.

Post-transfusion purpura responding to high dose intravenous IgG: further observations on pathogenesis

Summary. A typical case of post‐transfusion purpura (PTP) is described in a 61‐year‐old woman. Treatment with steroids corrected the purpuric manifestations, but the patient remained thrombocytopenic in spite of steroid therapy and plasma exchange. However, an intravenous infusion of high dose IgG led to a rapid and sustained increase in the platelet count.

Cephalosporin-induced immune neutropenia

Summary. Neutropenia is an occasional complication of treatment with cephalosporin antibiotics. This report describes two patients who had neutropenia while receiving high doses of cephalosporins. The neutrophil counts returned to normal after stopping the drug, and cephalosporin‐dependent neutrophil antibodies were demonstrated in both cases, using the granulocyte immunofluorescence test. In one patient, the immune neutropenia appeared to be due to a drug adsorption mechanism similar to penicillin‐induced haemolytic anaemia, while an immune complex mechanism may have been involved in the second patient.

Disappearance of HLA and platelet-specific antibodies in acute leukaemia patients alloimmunized by multiple transfusions

Alloimmunization by platelet transfusions was studied in 154 patients with acute leukaemia. 17 patients had HLA antibodies at initial presentation induced by previous transfusions or pregnancies; one of these also had platelet‐specific antibodies and one other patient had platelet‐specific antibodies alone. A further 38 patients developed HLA antibodies during therapy; three also had platelet‐specific antibodies and two patients developed platelet‐specific antibodies alone. Of these, 37 patients with HLA antibodies including three with platelet‐specific antibodies and one patient with platelet‐specific antibodies alone survived their initial therapy and formed the basis of this study.

Post-transfusion purpura associated with anti-Baka and anti-PlA2 platelet antibodies and delayed haemolytic transfusion reaction

Abstract. The occurrence of post‐transfusion purpura (PTP) in a 16‐year‐old girl with sickle/β‐thalassaemia is described. Clinically this was a typical case of PTP, but it was unusual serologically. Anti‐Baka and anti‐PlA2 platelet‐specific antibodies were identified and the patients platelets were typed as homozygous PlA1‐positive and Baka‐negative. The patient also developed red‐cell, granulocyte and lymphocytotoxic antibodies in response to the blood transfusion and had a delayed haemolytic transfusion reaction.

Use of chloroquine-treated granulocytes and platelets in the diagnosis of immune cytopenias

A chloroquine modification of the fluorescent antiglobulin technique has been used to demonstrate cell‐specific antibodies in the presence of HLA antibodies. This is of particular value in the diagnosis of alloimmune neonatal thrombocytopenia and neutropenia, post‐transfusion purpura, and in the investigation of febrile non‐haemolytic transfusion reactions and of patients refractory to platelet transfusions.