NEW DELHI: Of the 142 Tablighi Jamaat members who were quarantined at AIIMS, Jhajjar, 129 have recovered, and many of them have agreed to donate their blood for plasma therapy to treat Covid-19 patients in Delhi.Dr Sushma Bhatnagar, chairperson of Covid-19 services at the Jhajjar hospital, told TOI, “We requested some of the recovered patients to donate their blood, and they readily agreed. Now, we are working on the logistics for the donation and their stay.” She added that the Tablighi members had also agreed to give their blood sample for future research.Blood can be retrieved from a person after two weeks of recovery, said Bhatnagar. “Most of the Tablighi members are from outside Delhi, some of them foreigners. They cannot return to their hometowns during the lockdown. We will talk to the authorities on where to shift them and how to coordinate the blood donation,” she added.Plasma therapy involves transfusing plasma retrieved from the blood of persons who have recovered from Covid-19 into a person suffering from the disease. A 49-year-old patient admitted at Max Saket was the first Indian to undergo plasma therapy for Covid-19, and his doctors claimed it helped speed his recovery. The patient, who had been on ventilator for over a week, was weaned off the machine three days after going on the experimental therapy.With no known cure for Covid-19, countries are experimenting with drugs and therapies to treat infected people. Recently, four corona-positive patients at Lok Nayak Hospital and two at Institute of Liver and Biliary Sciences began plasma therapy as part of a clinical trial initiated by Delhi government. State health minister Satyendar Jain said on Saturday that four of the six patients who received plasma therapy have shown improvement in respiratory symptoms.At Lok Nayak too, doctors said most of the Tablighi members placed there in quarantine after evacuation from Nizamuddin’s Alami Markaz Banglewali Masjid in early April have recovered. “They’ve been shifted to the Covid care centre in Mandoli and Sultanpuri. Nearly 20% of those approached for blood donation have affirmed so far,” said Dr J C Passey, medical director of the hospital.There are at least 38 Covid-19 patients in Delhi who currently require ICU and ventilator support. Patients, during recovery, produce antibodies that attack the coronavirus. These antibodies are secreted by immune cells known as B lymphocytes found in the plasma, or the clear liquid part of blood that helps the blood clot when needed and supports immunity. Once a person has been infected and recovers, he or she develops antibodies that stay in the blood waiting to fight the virus should it return.Experts assert that blood drawn from a recovered patient can be used to extract plasma for transfusion into a sick patient. A donor's plasma can aid two patients, doctors said. The idea of using recovered people’s plasma to help patients has been used earlier, for instance during the outbreak of Severe Acute Respiratory Syndrome (SARS), also caused by a human coronavirus.